The way I see it is anything you buy should be ok to use in whatever you choose, be it commercial or not, as long as you are not redistributing the product as a freebie or for profit under your own name (therefore stealing) then there should be no problem. I personally would be quite flattered to find a character of mine pop up in a game but I must admit it would stick in the throat that I got $20 for the sale & the game was making a fortune :) As long as my products aren't being redistributed then please use them as they were intended, for your personal & commercial use.