It seems to me that the argument that it will help beginners learn correct intonation (so that they can subsequently go on to get rid of the 'training wheels') doesn't quite work.
When you play a fretted instrument, you press down on the string behind, not on, the fret. You can do this rather sloppily as well, so long as you mash the string down.
Without frets, you press very precisely and consistently at the precise point on the fingerboard which produces the desired tone. If you're at the wrong place--- wrong tone. If you aren't square or fret in any kind of soft fashion you can dull the sound.
For me, moving from a fretted to a fretless banjo wasn't just a matter of putting my fingers where I always did--- I had to adjust the position a bit. And I had to learn to hear the intonation in order to learn what was correct.
That, to me, seems to be the key thing--- hearing the intonation. The fiddle frets might help with that, but at the expense of training the fingers to go down further towards the peg-head than they're supposed to and to be rather imprecise besides. So the student trained with frets may know he or she sounds like hell without them, but may have quite a learning curve to gain back what is lost, what with retraining all those brain cells and nerves to do something very different without the frets.