It's for people with pull; not drifters (3)
I believe the answer is:
'it's for people with pull' is the definition.
I can't tell whether this definition defines the answer.
'not drifters' is the wordplay.
'not' becomes 'o' (I've seen this in other clues).
'drifters' becomes 'ar' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
Can you help me to learn more?
(Other definitions for oar that I've seen before include "Pusher" , "that may be feathered?" , "Crewman" , "Rowing blade" , "Rower's implement" .)