Yep, I can concur that using both is fine.
Better still, if you have a graphics card and you configure your RTG not to close down / promote PAL/NTSC stuff, you can have a pal monitor and your gfx card all going at once. I did this to run some old speccy emulators that wouldn't promote to the RTG screen.
It's actually fun seeing two screens doing stuff simultaneously :-D
