I'm trying to figure this out. I bought a used MBP that came with ML installed
Do you mean it was shipped new with ML? If so, it won't run Snow Leopard.
If not, see what model it is (Apple logo in your menubar > About this Mac > More Info) Under where it says MacBook Pro should be the size and build period.
Compare that to this: Mac OS X versions (builds) for computers to see what it shipped with. If it shipped with Lion or later, it won't run Snow Leopard.
What I would like to do is use Migration Assistant to move the Adobe software and a few other items in my Applications folder to my old iMac (21.5" C2D 3.06ghz, SL 10.6.8) via firewire.
Sorry again -- you can't go "backwards" with Migration Assistant. If the versions of the apps will work on Snow Leopard, you'll have to reinstall them from scratch (ie, the original discs) on the Snow Leopard Mac, then manually copy the files.