If its never worked in fs2_open thats an important thing to mention.
I'm not sure, I'll make a point of testing the 3.5.5 release I have, since I was using the most recent _t version when I noticed there was no FF. I've never used a version previous to 3.5.5 though.
(Edit: Ok, stock 3.5.5 isn't giving Force Feedback either)
(Edit2: Posted on Bugzilla
http://fs2source.warpcore.org/bugzilla/show_bug.cgi?id=124 )
(Edit3: Just to make me look like a dumb idiot, Force Feedback came alive again. The only change I've made is to reduce the center spring strength (The joystick seems to fight itself and starts shaking when center spring is too high), and now FSSCP seems to do FF perfectly. Oddly FS2 1.20 was still force feedbacking regardless.. I've added a note to the bugzillla entry, saying that reducing center spring seemed to bring FSSCP back to life, so maybe this can be ignored unless others have a similar problem, I do apologise)