You could run it in 4CM or "4 cable method" which enables you to use the GT-10 for both before and after preamp effects.
To hook it up, you go
Guitar>GT IN>GT SEND>Amp In
Amp FX loop Send>GT Return
GT OUT>Amp FX loop return
Turn on the DC's loop and the GT's internal loop and viola, you now "hugged" the preamp with the GT-10.
With this configuration you can
- use effects before and after the preamp; use the GT FX chain to arrange your effect order, the amp's preamp is the "S/R" block
- use the GT-10 as a preamp (though if you ask me the preamps on the GT aren't that great)
I hope I was clear enough. But to answer your question yes you can use the GT in front, just select the Output accordingly and try to match the levels of the patch and the GT in bypass - the way I do that on my GT-6 is dime the output pot and use the internal patch level to determine signal level.