I have a new iMac, but I need to revert back to OS10.7 for software compatibility issues at work. Will the fusion-drive function properly?
The problem here is not only the Fusion drive but the new iMac hardware as a whole. Older OS X versions usually do not work on hardware released after the release date of the respective OS X due to missing drivers etc.
Alternatively you could try to install 10.7 in a virtual machine.