When is a verb impersonal?
Basically, when its subject is an infinitive, a clause, or a neuter pronoun that refers to an action or fact rather than any concrete object. (Or one of these types of subjects can also be left implied.)
For instance
oportet = "it is necessary or proper" cannot take any noun as a subject, only an infinitive, a clause or a neuter pronoun, e.g.
abire oportet = "it is necessary to go" ("one needs to go");
oportet eos dormire = "it is necessary for them to sleep" ("they must sleep");
hoc oportet = "this is necessary" in the sense of "this (= some action) should be done"; it can't refer to any concrete object.
Patet isn't always impersonal, but in the way it is used here I think it can be called so.
Does it change the translation of the accusative-infinitive construction.
Not in this case.