If you have a raw water cooled engine and that's how he winterized it, I would:
make sure you have an invoice indicating what was done if there is a problem in the spring
if you can, take a sample from each block drain to make sure there is really AF in the engine!
it has been discussed many many times, the danger of using the suck AF up the drive method, if the engine is not drained first or the 'stat not removed first. If he did either, then OK, if he did neither, then I'd check the drains.
I think for the Bravo or Volvo pumps to prime, its best to have a pressurized flow, gravity may or may not be enough, if you can jack the front of the boat down as far as you can get it that helps, I would add a pump to a winterizing tank if I used one (on a closed cooled engine only, that is).