Can't see why learning from multiple sources should be an issue. I would continue with GT gf2 because, no matter what other sources you use you know the GT gf2 will be giving you the correct techniques etc.

I have used videos of original artists as well as some free tutorial youtube stuff where there is a song I like, but GT doesn't cover it. But I will still continue to use GT as my main source of lessons and songs because they are the best in my opinion.

The only time this might be a problem would be if there appears to be conflicting information (maybe the key of a song, techniques being demonstrated etc) in which case I would default to GT.

I can't see a problem at all.