Purely personal opinion here...take it for what it's worth...

In the sense you asked the question, yes, I think the plane is probably "important", but it doesn't necessarily need to be what someone else (or common wisdom) might dictate as a "good trainer".

The typically recommended trainers (The Telemaster style...high flat bottom wing, lots of dihedral, low control rates, able to fly very slowly, etc) have, obviously, certain traits that make them good choices for many students. The ability to fly very slowly reduces the chances of stalls while learning to land, for example. The dihedral tends to make the plane want to fly straight and level...advantageous for new pilots who might get disoriented easily, and so on.

This doesn't, by any means however, mean that they're the only suitable airplanes to learn on. For all extents and purposes, I learned on an Electro-streak and Super Stick...and I've trained plenty of guys on the Mustang PTS, and even trained one TO SOLO on an Ultimate Bipe.

What's "important", imo, is that the airplane not have any nasty surprises in store for the student....that it does what he expects "an airplane" to do. To be certain, for the VAST majority of students, this means "traditional trainer", though the line is blurring a whole bunch the last few years with the sims.

That was the case with the guy I trained on an Ultimate. he LOVED the plane, had spent HOURS with one on the sim, and after one flight on a "traditional trainer" he was frustrated...it simply didn't act like he thought a model airplane should. Given that his "experience" was ENTIRELY on an overpowered bipe, its no wonder. We tried a Sig Somethin' Extra next and it was "better" in his opinion, but still did things that didn't feel right. "It glides forEVER...how can i ever land it?" he said.

Since I had access to a .40-sized Ultimate at the time, I thought "Why not? I'll just be extra-quick to take the airplane, let's give it a shot." and we put him up. He was in hog heaven, and soloed just 2 weeks later...on that very same Ultimate.

*shrug*

Probably a longer answer than you wanted...and by NO means do I suggest that people should go grab an Ultimate as a trainer...just that it sorta illustrates one of my points above. Have an end-point and a bag of tricks.

Whatever gets 'em flying, right?