Yes, your frame could be weakened... It's tough to say, really.

It depends upon what kind of strain that that part of the frame is subject to. It also depends on if there is any damage that you can't see.

Either way, a gouge like that is indeed a stress riser, which could lead to cracking down the road. But this still depands on what I said above.

Is it safe to ride? I really wish that I could say, but I can't. Your best bet is to take it to a good frame maker and get their firsthand opinon.

In any case, if you start to hear any pinging or ticking coming from your frame, stop riding it! Those sounds would qualify as potentially very bad...

I wish I could offer you more help...

-Erik