The % of UDFA RBs who see 3 years on a roster in the NFL is miniscule. From that perspective, Tucker has already beaten the odds.
In terms of whether he'll ever be relevant in FF, it feels like we'll just have to wait and see. Irving was a surprise home run last year and White is a decent NFL player, so Tucker has just kind of been stuck there without great opportunity. That they aren't forcing touches suggests they don't love him, but he wouldn't be on the 53 if they thought he was JAG level. Once you get past the elite backs in the NFL, there's a big glut of guys who can put in a shift when called upon, but aren't exciting enough to command steady work.
At the moment Tucker seems to be stuck in this Jordan Mason/Keaton Mitchell type of territory.
I wouldn't go out and pay a premium for him in dynasty, but he remains an intriguing stash IMO.
Looks to be a FA after this season if I'm not mistaken. Demand for his services should be telling, one way or another.