I've only ever dealt with contracts rather than a release form. It is usual practice to have a contract with a composer rather than a release form because of the added complications of copyright licensing. Providing the artist/composer signs a document with a clause stating that all their work is original and granting you a licence to use his/her material, you are protected against being sued for breaking copyright law. Or rather, depending on your local legal system, you might still be sued by the copyright holder and then you would have to sue the composer for your expenses and whatever amount the court awarded the copyright holder. So you are protected ultimately, though certainly not in a hassle free way!
Even if the copyright holder goes after the composer directly, rather than you (the production company), you are NOT "in the clear"!!! Regardless of who is sued, your film still contains un-cleared copyrighted material. So the Copyright holder could serve you with an injunction to stop you screening, selling or distributing the film until you either obtain copyright clearance or remove the copyrighted material from your film. Obviously the copyright holder has you over a barrel to an extent and will likely demand a hefty price for copyright clearance. In theory, you would then have to sue the composer for any costs or losses you incur from having to obtain clearance or remove the copyrighted material.
Caveat: I've had a fair bit of experience over the years with the legalities of copyright but I'm not a lawyer.
G