This NFL document seems to say that yes, they can:https://www.nflregionalcombines.com/Doc ... 0Rules.pdf
The first rule says men can be eligible once they're past college eligibility, which the document specifically says can be ended with signing to another professional football league.
I don't think this is correct....citing 2 paragraphs from your link...
COLLEGE ELIGIBILITY. All college football eligibility of such player has expired
through participation in college football (expiration does not include a loss of college
football eligibility through withdrawal from school, dismissal or signing of a professional
contract in another football league). Or,
[urlTargetBlank]PLAYER NOT ATTENDING COLLEGE. Any player who does not attend college is
automatically eligible for selection in the next principal Draft that is conducted after four
NFL regular seasons have begun and ended following either his graduation from high
school or graduation of the class with which he entered high school, whichever is earlier. If
four football seasons have not elapsed, he is ineligible for selection, but may apply to the
Commissioner for Special Eligibility pursuant to the conditions in the section below entitled
If said player is not selected in the Draft for which he is eligible, he is
eligible to be signed as a free agent, unless he subsequently attends college and participates
in college football. In such event, he shall become subject to the rules that are applicable to
players who attend college. Or,[/urlTargetBlank]
This second paragraph seems to allow commissioner flexibility, so I assume it may be possible for someone who would otherwise be ineligible and perhaps did well enough in the XFL could apply for eligibility. I would think the commissioner wouldn't make exceptions for all XFL players, but may on a case by case basis.