If we wanted to say single driver it would be like this, right? - Welchen zuständigen Fahrer will er?
Yes.
Why welchen in singular male and not welcher? It's Nom. case.
It's not nominative. "Er" is nominative. He is wanting the driver(s), so "welche(r)" is accusative.
Tripped up here. Thanks for clarifying.
Would German ever say "Welche der zuständingen Fahrer will er?"