Sure they can. After seeing the broad spectrum of approaches on here and in my local community, the only thing I truly feel is a minimum requirement to be polyamorous is the ability to engage in multiple intimate/romantic relationships simultaneously.
Nothing says you have to actually be in multiple relationships. That would be like saying you're only gay if you actually have a partner of the same sex right now.
Playing the Game of Life with Monopoly rules.
Monogamy might just be in my genes
Poly Events All Over