Can it be vaguely true that God believes p? Maybe not. For if it's vaguely true that God believes p, then God is unable to have perfect self-knowledge. Perfect self-knowledge requires definitely knowing, for every proposition, whether one believes it and if so how one believes it, and more generally what one's doxastic attitude towards the proposition is. This means that God will definitely know, for every proposition, whether he definitely believes, or whether he has for it the doxastic attitude appropriate to cases of vagueness, or whether he definitely does not believe it. But God's beliefs perfectly mirror reality. So, in particular, for every proposition, God will definitely know whether that proposition is definitely true, vague or definitely false.
It follows that if God exists, then there is no higher order vagueness, except perhaps epistemically for us: it is never a vague matter whether a proposition is definitely true, vague, or definitely false.
But the arguments for higher order vagueness are just the same as those for first order vagueness. So if we're going to bite the bullet and accept that higher order vagueness is merely epistemic, maybe we should bite the bullet and accept that first order vagueness is merely epistemic, too.
I suppose the point to attack here is my notion of perfect self-knowledge. Still, the following remains true (and I got this general idea from Jon Kvanvig): it's a puzzling question what sorts of epistemic attitudes an omniscient being is to have towards vague truths.