Polyuria is a common symptom of diabetes mellitus?

Yes, but only in untreated diabetes.

Polyuria (frequent urination) is part of a classic triad seen with untreated diabetes mellitus. This triad includes polyuria (frequent urination), polydypsia (frequent thirst), & polyphagia (frequent hunger). This triad is often seen with the paradoxical combination of polyphagia and weight loss.