It's not so much hooked as an adjective, but hooked up as an idiom and verb.
Hook can be used as a verb that means (from my OED):
Hook verb - grasp or catch with a hook; fasten with a hook or hooks.
When you hook things, for example
I hooked my TV to my XBox.
you are joining them together by some means. This can equally be expressed as
I hooked up my TV to my XBox.
When it comes to one person hooking up another with something, as in your example, the joining together is a euphemism for giving something to someone. So the example can be read as
His brother threw him this bachelor party.
Also, another example would be
My man Dexter here hooked me up with this sweet ride.
Indicating that Dexter gave the speaker a nice car.
Hooked up can also have racier connotations, which I don't think are present in your example.
I hooked up with Clarice again, last night. Man, she goes like a train!
Where hooked up implies sexual intercourse. Here, I think, the analogy to joining is obvious.