Do I understand correctly that the sentence would not have the macron on the final i of "dovaogēdī" if it were about a single Unsullied?
Would this naturally cause a garden-path-like situation to listeners?
No, because of the stress. Stress isn't marked in High Valyrian, but it is, in fact, crucial. Valī stressed on the last syllable is accusative plural; valī stressed on the first syllable is nominative plural conjunctive.