hmre p. 116 " there seems to be a mechanism that divides those who are called to serve as nightwalkers, and act as their community’s guards, from the Gifted whose supernatural taint prevents them from integrating with society. "
so apparently the Gift and the nightwalker virtue are mutually exclusive.
in addition the nightwalker concept, while certainly interesting, would require potentially running multiple fertility battles every year, which would bog the game down significantly, as well as removing the covenant wealth variation rules from the modifications that I am using.
Ecstatic Magic is apparently a folk magic mystery, requiring initiation even after Gifted Sorginak have been opened, so it would not be appropriate either.
The main issue seems to be that spirit walking is, in Ars magica, generally an advanced form of magic, and may be something the character could pursue after their gauntlet, or you might decide to keep this idea for a future character as other tribunals open up in the game.