Can a god have more than one blessed vessel?
Short answer, yes.

I would say that it is possible for a god to have more than one hafuri, because to be a hafuri only means to attempt to sacrifice one's name for their master. I don't believe there is a limitation on that, however as far as I know there can only be one exemplar/guidepost. Exemplars and blessed vessels are different though (as Takemikazuchi reminds us frequently).

In one arc (warning: manga spoiler!),


   Bishamon makes Nana, who was a legendary blessed vessel imprisoned by heaven, her shinki, so it is possible for a god to have more than one hafuri. However, Nana changed and became a hafuri for her original master and not Bishamon, so there is no definite proof.