I have 2 guys, both capable of playing LF that I'm planning to use at LF and 1B. The more injury prone player is a slightly better fielder. Is he less likely to suffer an injury if I play him at 1B?

Logic would say, 'Yes,' but I'm not sure there is any coded increased risk to injury based on position.

I would hope that injury was governed by the health rating, and not so much by the position played.

I have noticed that position effects fatigue and not just PA's or innings played.  Not sure about injury risk.  I don't have hard numbers but I do have a player that when playing LF all year dips below 100 fatigue much later than when he plays CF all year.  He can log about 550 AB's a year in LF, and about 400AB's in CF.  Could just be an aberration as he is early in his career, but the two seasons are there.

It is my impression that 2Bs are much more likely in HBD to have catastrophic injuries than other position players, but that's just an impression.  If it's a correct impression it would be mimicking many people's impressions of real baseball; there just seem to be a lot of 2B that break down early in their careers.  But I have no data on real baseball, either.