I do exactly what you describe - load up Giga VST Adapter in forte, and run GS3 on the same machine. Works great for me.
The only catch is that forte doesn't handle multiple outputs from synths, so you are limited to 1 stereo pair coming out of Giga. This may not be a problem for you, but it is for me because I use GS3 for electric guitars (among other things) and I need to run an instance of Amplitube or other amp sim on each guitar part. I have had very poor results using VSTs in GS3.
The way around this is to get EnergyXT ($50), which is a VSTi that, among other things, can host other VSTi's. That way, you load up eXT in forte, then run GVA from within eXT. You can now access as many outputs from GS3 as you want in eXT, and place effects wherever you want them. You then have 1 single output pair from eXT to forte, but that works fine for me.
You may ask why I don't just use eXT standalone and forget about forte altogether. That would be fine in a studio setting, but I use this setup live. Forte has an awesome feature, which no other software has, called Scenes. You can save particular configurations of your rack (mixer levels, effects settings, synth settings, etc.) as scenes, then quickly change between them. I have a different scene for each song. It's like completely reconfiguring an entire rack of gear in less than a second. Forte handles the scene changes very intelligently. For example, you can specify synths that should not have their config data sent with every scene change. This is great for samplers like Kontakt, since reloading a large sample set would make the scene change take several seconds.
So if I loaded up GigaVST in Forte..started up GS 2, then opened up EW Gold as a VSTi in Forte, would I get a conflict because GS2 and EW Gold would be trying to access the same stereo outs?
Is that what you're saying?
You dont have to run Giga as a vst in BF or V-stack. They can run side by side. Just give them there own ports. e.g. GS2 midi port 1 (adat 1/2), Brainspawn or v-stack ~ midi Port 2 , 3 , 4 (adats 3-9). I think you have to run GS first. Thats how I do it...Rich
Rich is right in that you don't really need to run Giga through GVA, but I have always had problems trying to run Giga and another audio app on the same card, even if they use separate outputs. I also prefer being able to bring the audio from Giga into forte (or Sonar, whatever), so I can run effects on it in real time. This is especially true for Giga 2.5 since it can't host VST's like Giga 3 can.