Learn Italian: Volevo un autografo, ma il ragazzo dello staff non mi ascoltava. - I wanted an autograph, but the staff guy wasn't listening to me.

No. The hypothetical imperfect replaces the subjunctive or conditional in unreal situations (like Se lo sapevo...). Here, volevo is stating a real fact in the past—you genuinely wanted an autograph. It is the standard use of the imperfect to describe a past state of mind.

Could volevo also be the 'polite imperfect' here?

Yes! While it functions perfectly as a past tense narrative ('I wanted'), it is also exactly what you would have said in that moment to be polite: Volevo un autografo ('I would like an autograph'). When recounting the story, that polite request naturally doubles as your past narrative.

Why is the article dello used before the English word staff?

Foreign loanwords in Italian keep their original spelling but take Italian articles based on their starting letters and gender (most are treated as masculine). Because staff starts with an s followed by a consonant (st-), it requires the article lo. Combined with di, this becomes dello.

Why use the imperfect non mi ascoltava instead of the passato prossimo (non mi ha ascoltato)?

The imperfect is used here to describe an ongoing background situation rather than a single completed event. You are painting a picture of the scene: while you were standing there wanting an autograph, the staff member was continually in a state of ignoring you.