I'm doing just that, using a JTV (89 in my case) and a trem 700 as a backup, or I did last summer...
The thing is... the sounds are there, but they're not the same, so, as TheRealZap said, you'll probably want to setup a different setlist for the 700.
I would just use the 700 whenever I would break a string on the JTV, and the same models did sound a bit different. Even my own custom variax models
sound different on the two guitars. In addition to the change in the way the models sound, I use the bridge position of the magnetics a lot, because
they respond to palm muting just as any normal humbucker should, and that is something the 700 can't match (stock 700, that is).
So, unless I can afford a new JTV (those new JTV89F got me drooling...) I'll stick to what I have, and I'll have to use different setlists for each variax, but...
if you want to use the same list and recall whatever model on each, YOU CAN.The HD500 edit lets you store different settings for different instruments.
The same patch can recall different models (and tone positions and whatever parameters are available on the instrument) on different kinds of variaxes.
If I have the JTV plugged, the patch calls whatever model I have set the "Tyler Variax" section on the VDI input drop down menu to call, and when I have
the 700, it calls the model set on the "300/600 500/700" section. They're independent.
So yes, HD500 will support both, and on the same patch, but, being different in sound, it's preferable to dedicate a different setlist to each.