While I'm not terribly familiar with the PUA literature, based on your description I would say that most definitions of polyamory exclude it. There's a great deal of scorn in the poly community for relationships with a "one-penis policy," as well as a general emphasis on egalitarianism.

Actually, PUA discussions of MLTR (at least the few I've seen) seem to completely ignore the question of whether the women involved have other partners or not, although I suppose that is not strong evidence in either direction.

Perhaps the authors assume that "of course" exclusives are the default (and thus don't mention it), or perhaps they assume that "of course" things should be egalitarian by default (and thus don't mention it).

(And of course, there may be discussions I haven't seen, since my limited study of the PUA field is focused mainly on personal development and in-relationship applications, and limited to free materials almost exclusively.)