I'm reluctant to pay my friend's roommates for staying at their house for 2 nights
Has he discussed this with you?
Yes, with me, but I don't think he talked to his roommates about it.
Maybe he OKed with them. If not, I understand why you'd feel uncomfortable being around there since you haven't paid the roommates yet.
Don't you think that it's sort of unnecesary for me to pay the guy?
If the agreement was for you to pay to stay there, then you should honor your commitment.  You may find people are unwilling to help you in the future if you refuse to uphold your end of a bargain.