Not the same thing. You know this, c'mon.
Kicker first.
A kicker or a punter in the USFL/UFL has no opponent on the other side of the line fighting with him for advantage. The only difference between kicking a 53 yard FG at Legion Field versus doing so in AT&T is the possible intimidation factor of having such a larger audience. This is why I was quite possibly the very first poster on this board to ever mention the possibility that the Birmingham kicker known there as Aubrey-matic could be worth a look... why wouldn't you take seriously a kicker who was doing well there?
Now let's talk punt returner. Yes, it's more difficult than K or P to make an NFL team, but it's still something different than making an NFL team at an offensive or defensive position. While you can't say, as was said above, the PR has no opponent on the other side fighting with him for advantage, you can say that the skill set required to be a good punt returner more expeditiously translates because the punt play itself doesn't vary... you always have the same basic elements every time. And the speed of the game doesn't even change substantially, largely because it's so much more about timing, given the fact you can't even be hit (legally) until the ball falls out of the sky into your hands.
It is reasonable, then, to think that players who excel in those two roles are particularly well-postured to do well if they get a chance with an NFL team in need.
Not the case with the non-special teams positions. So much greater difficulty because you routinely are being challenged straight-up by at least one opposing player who might be faster or stronger or smarter than you, or sometimes all of the above, hence the fact that those are the players who tend to get drafted and, then, who tend to stick. The UFL success you may have had is so much more likely to be a function of the fact you weren't having to compete against NFL quality players snap after snap after snap.
I'm not being dismissive of the LB and CB we just signed out of some obstinate attitude, but out of simple, objective logic.