Pete,
I think that's a good plan (to pull those two new NB trees in 1g into the house). Tough to say for sure how they'll do with dormancy... if they're already dormant though, then let 'em. In my (limited) experience with potted trees, even the small/young ones do OK being dormant... they just can't handle the lower temps that a bigger one can. I guess they've probably got to have some minimal threshhold of potential energy stored up though... that's why I don't really want to root late-season cuttings (rather hold them over for springtime). I see lots of folks on here that "force" new rootings through a winter without dormancy by using lights... I still rely on sunlight primarily though, and that's why I'm sold on letting dormancy happen. Like I said, even very small trees seem able to deal with dormancy as long as you don't let 'em freeze and keep them minimally watered. (I've had lots in 4" pots that went dormant and came back... it was back when I was less careful and deliberate about figs... they survived though, and I've got some very small trees that I kept small on purpose still in small pots, and they'll be dormant this winter, though I'll probably give most of them away to fig friends). Good luck with the Niagara Blacks.
Mike central NY state, zone 5