The key to this is, if the player knows someone will be playing position A, but starts him at position B, he's going against the spirit of the game on purpose because the site has a loophole.
But the problem is that #1 and #2 are both correct. He has played the same number of games at both positions to this point.
Let me simplify it..What position is Webb playing in week 15? What position (are you) starting him at?
If those 2 questions don't have the same answer, I wouldn't allow it.
Bad sportsmanship.
Careful you don't fall off your horse...

It's not always that simple. He was drafted as a WR, has played some WR, but they are also experimenting with him at QB since he's such an athlete. We're seeing it more and more already. Brad Smith is a WR, but gets snaps at QB quite a bit. It's very possible that you could go into a game with him as a WR and due to injuries he ends up QBing for most of the game. It's not bad sportsmanship, it's the rules not evolving with the athletes.
A progressive commish would already be on top of equalizing the scoring system so that there's no bonus to having Webb at QB, WR, or even PK. It's the wave of the future to have athletes on your offense instead of positional players. Why not take the opportunity to get your league rules up to snuff as well?