Hi!
LMMS can load Sf2 files.
While a GIG player is coming in lmms 1.2
The reason why it crashes with that VST may be because GIG sample packs are really big. So, how much MB are yours?
Also, when loading a really big file inside of lmms, just give it time, even minutes, and if you want check your RAM behaviour to see if it's really crashed or if it's loading!
This may be different between OSs
For example, I tried this new Gig player and loaded a 500MB sample pack. The program did not respond for like two minutes, and then it worked again and I could play the gig file!
Last thing: are you on a quad core CPU? LMMS and VSTs work better together on a multi-core. For some reason xD