Yes; you'll probably have to change the tuning, though. And if there are more than four strings in the track you want to play, you'll have to set the redundant strings to ridiculously high or low settings before you remove them entirely(Which should move all notes there to different strings).
One problem you might encounter would be notes that don't fit in the ukelele's range, which TG will remove from the track entirely(So you'd probably have to mess around with moving notes to different octaves), and the fact that TG always uses a fretboard length of 24 frets(Although it supports notes up to the 30th).

Overall, making any given track playable on a ukelele should only take a few minutes maximum.

EDIT: Also, just to make sure everyone knows, despite its name, Guitar Pro is designed for basically all instruments(Mainly guitars, basses, drums, and keyboards, but it's supposed to work for all of them; the only big difference between Guitar Pro and TuxGuitar -- other than price and Linux support -- is that GP has the "Realistic Sound Engine", while TG is MIDI-based)
(Next time I make a post in this thread, I'll try be more concise... :L)