Possibly...not trying to be awkward, but I can't get it to crash any more! I may have updated Multiply or CbB since I last used it - I'm using the VST 3 version and think I was using the VST 2 version when I was getting the crashes.
They are DirectX plugins so don't need to be (VST) scanned by an application. If FL doesn't support DirectX plugins, you can't use them in it, scanned or not.
It is in normal DAW parlance but remember Reaper has a language all of its own! I think the OP just wants to render to dev/null instead of a file as writing to disk is perceived to be a bottleneck: I'm not sure I buy that assumption though, at which point the request becomes moot (do a faster than realtime bounce would surely be what is wanted).