Mercury markets some very good oils, their 25W - 40 synthetic blend is good stuff, I wouldn't hesitate running in a VP.
As for it being just a GM motor, yes VP and Mercury do obtain their engine from GM, GM does build the engine for marine usage. That does not mean the oil specifed is the same as in automotive use. There is a FC-W certification for marine oils.
FB-00210R Outboard 500 4T SAE 10W-30 YACCO SAS
FB-00211R Outboard 500 4T SAE 25W-40 YACCO SAS
FB-00511J Yamalube Marine Performance FC-W 10W-30 Yamaha Motor Corporation, U.S.A.
FB-00512J Yamalube Marine Performance 4M FC-W 20W-40 Yamaha Motor Corporation, U.S.A.
FB-00604J West Marine Premium 4-Cycle Outboard Oil 10W-40
West Marine Products, Inc.
FB-00616J Lubrax Nautica Tecno SAE 25W-40
Petrobras Distribuidora S.A.
FB-00620K Yamalube 5W-30 Full Syn Marine FC-W
Yamaha Motor Corporation, U.S.A.
FB-00624L 25W-50 Semi-Synthetic Blend
Sierra International LLC
FB-00625L 10W-40 Semi-Synthetic
Sierra International LLC
FB-00626M Power R 4T Outboard
PTT Public Company Limited
FB-00627N MotoMaster Formula 1 Synthetic Marine 10W-30 Outboard Engine Oil
CITGO Petroleum Corporation
FB-00628N Mystik JT-4 Synthetic Blend 4-Cycle 25W-50 Marine Engine Oil
CITGO Petroleum Corporation
FB-00629N Mystik JT-4 Synthetic 4-Cycle 10W-40 Marine Engine Oil
CITGO Petroleum Corporation
FB-00630N Mystik JT-4 Synthetic Blend 4-Cycle 25W-40 Marine Engine Oil
CITGO Petroleum Corporation
FB-00631N Mystik JT-4 Synthetic 4-Cycle 10W-30 Marine Engine Oil
CITGO Petroleum Corporation
FB-00640P Quicksilver High Performance 25W-50
Mercury Marine
FB-00641P Mercury High Performance 25W-50
Mercury Marine
FB-12457P Wave Rider S Outboard 10W-40
Bahrain Petroleum Company
FB-13092U Repsol Nautico Gasoline Board 4T 10W-40
Repsol Lubricantes Y Especialidades S.A.
FB-13103U INA Outboard 4T SAE 10W-30
INA MAZIVA Ltd.
FB-13721U MARINE 4 TEMPS FC-W 10W-30
Minerva Oil SAS
FB-13724U ECSTAR V7000 Semi-Synthetic Marine Engine Oil
Suzuki Motor Corporation
FB-13800W MOTUL Marine Tech 4T 25W-40
MOTUL S.A
.
FB-13827W Marine Inboard Four-Stroke Oil 25W-40
Penrite Oil Company
FB-13852W Suzuki Marine 4-Stroke Engine Oil 10W-40
MOTUL S.A.
FB-14307W Marine Performance 20W-40
Yamaha Motor Canada Ltd.
FB-14800W MOTUL Outboard Tech 4T 10W-40
MOTUL S.A.
FB-20071R Outboard 4000RS 25W-40
IPONE
FB-20114N Evinrude Johnson Marine Stern Drive 25W-40 Oil
BRP U.S. Inc.
FB-20123R KATANA JET 10W-40
IPONE
FB-20208M Avia Outboard 4T 10W-40
Avia France
FB-20215R Outboard 500 4T SAE 10W-40
YACCO SAS
FB-20230R JET 4000RS 10W-40
IPONE
FB-20240R Outboard 4000RS 10W-40
IPONE
FB-20333H IGOL Prosurf 4T FC-W SAE 10W-40
IGOL France
FB-20444H IGOL Prosurf 4T FC-W SAE 10W-30
IGOL France
FB-20555H IGOL Prosurf 4T FC-W SAE 25W-40
IGOL France
FB-20601L Titan Marine FC-W
Fuchs Petrolub SE
FB-21004J 10W-30 4-Stroke Outboard
Sierra International LLC
FB-21005K 10W-30 Synthetic 4-Stroke Outboard & Stern Drive
Sierra International LLC
FB-30220H SUPRA 4
Eduardono S.A.
FB-31001B Tohatsu Premium Four-Stroke Oil
Tohatsu America Corporation
FB-37565U KPO Jet Ski Watercraft 10W-40 4-Stroke Oil
Kawasaki Motors Corp. USA
FB-38003W MOTUL Outboard Tech 4T 10W-30
MOTUL S.A.
FB-38525W Suzuki Marine 4-Stroke Engine Oil 10W-30
MOTUL S.A.
FB-39045W CEPSA Outboard 4T
CEPSA Comercial Petroleo SAU
FB-40003A RAVENOL Outboardoel 4T
Ravensberger Schmierstoffvertrieb GmbH
FB-42111T Liqui Moly Marine 4T Motor Oil SAE 10W-30
Liqui Moly GmbH
FB-42112T Liqui Moly Marine 4T Motor Oil SAE 25W-40
Liqui Moly GmbH
FB-43069W Marine Full Synthetic 5W-30
Yamaha Motor Canada Ltd.
FB-43072W Marine Performance 10W-30
Yamaha Motor Canada Ltd.
FB-44201N Power Boat 4 (SAE 10W-40)
Comercial Importadora, S.A. de C.V.
FB-44215K 25W-40 4-Stroke Stern Drive
Sierra International LLC
FB-44216K 25W-40 4-Stroke Inboard & Stern Drive
Sierra International LLC
FB-44221R Power Rider 4T
Comercial Importadora, S.A. de C.V.
FB-44228J Honda Marine 10W-30 Engine Oil
Idemitsu Lubricants America Corporation
FB-44303J Gulf Pride 4004 - SAE 10W-40
Gulf Oil International
FB-44404M MPM Marine FC-W Engine Oil 4-Stroke Outboard EHP 10W-40
MPM International Oil Company B.V.
FB-80114J West Marine Premium 4-Cycle Outboard Oil 10W-30
West Marine Products, Inc.
FB-80116J West Marine Premium 4-Cycle Outboard Oil 25W-40
West Marine Products, Inc.
FB-80460T Yamalube Marine Performance FC-W 10W-30
Yamaha Motor Distribution Latin America Inc.
FB-80812K RAVENOL Outboardoel 4T SAE 25W-40
Ravensberger Schmierstoffvertrieb GmbH
FB-80813K RAVENOL MARINE OIL PETROL SAE 25W-40 Mineral
Ravensberger Schmierstoffvertrieb GmbH
FB-80814K Nautic 4T SAE 10W-30
Comercial Roshfrans, S.A. de C.V.
FB-80815K Nautic 4T SAE 25W-40
Comercial Roshfrans, S.A. de C.V.
FB-83138K RAVENOL Outboardoel 4T SAE 15W-40
Ravensberger Schmierstoffvertrieb GmbH
FB-83139K RAVENOL Outboardoel 4T SAE 10W-40
Ravensberger Schmierstoffvertrieb GmbH
FB-83140K RAVENOL Outboardoel 4T SAE 10W-30
Ravensberger Schmierstoffvertrieb GmbH
FB-83180R Suzuki Synthetic Blend Marine 4-Cycle Engine Oil SAE 10W-40
CITGO Petroleum Corporation
FB-84000K CEPSA Fuera Borda 4T
CEPSA Comercial Petroleo, S.A.U.
FB-85003K Quicksilver Synthetic Verado 4-Stroke Outboard Oil 25W-50
Brunswick Marine in EMEA