If the tracks you submitted are financially viable, I'd say buy the libraries so that you can have the licenses if needed. If your producer friend has charged you money for his/her work, deduct the libraries expenses from his/her cut. EDIT: If you decide to buy said libraries, read the fine print in the license agreement before you invest your bucks. There could be some limitations.
you have to be specific on how those samples were not cleared. edit: i see now you didn't receive any complains at all from your label, so that is the problem? the chances that anyone will ever care about where you got your samples from is remote, specially if they are from a sample library meant to be used like that. if you or your friend had sampled them from another record, that is a totally different thing. Last edited: Nov 19, 2017
Thanks for your reply! You are right. Maybe that's my only chance to release my tracks if I buy the libraries. My "friend" gave those samples for free, so I can't do anything with him in this case Buying these packs are not that big problem, since I'll probably get more money from the label when they sell my tracks.
What kind of samples? Just some synths, I would not worry about it. I used some vocal samples in a track, and I bought it after I sent it around just in case, because those vocal samples, phrases etc, they are really unique, but a sound of some synth, as you said, you could recreate them yourself, in which case, I would not worry about them. But if you can buy them, maybe it will make you feel better.