Yes, it's no problem using several versions of FrameMaker on the same computer. I've had versions 8, 9, 10 and 2015 sitting on the same PC without any issues, however, these are the common caveats:
The other gotcha with multiple versions installed is Windows knowing what application to launch if you open a .fm or .book file directly. Generally, it will be whatever version was installed last, but this can get screwed up.
Thanks for your prompt responses!