If you were omniamorous I would think that would include the potential to go through phases of being asexual/aromantic. I think that many polyamourous people have the potential to be satisfied in a single relationship. Just because one has the ability to love more than one does not mean that they need more than one love at all times throughout thier lives.
I think that it would still be important to have the discussion that you are poly when entering a single relationship if you are aware of your ability to love more than one at a time. Even if at the onset of the relationship you have no desire for anyone else and can't imagine ever wanting another relationship again. Things change over time and the other partner is going to feel decieved if down the line you connect with someone else.
Everything will be ok in the end. If it's not ok it's not the end.