EPDM is pretty inert stuff. I've not worked with butyl flashing tape, so I' not entirely sure about its composition, but from what I've read, it is a butyl adhesive, which means it is probably made from polyisobutylene and some tackifiers. It's the tackifiers that I would worry about, as they could leach from the adhesive into the EPDM, softening it.
What is the application here?
Find a good adhesive for EPDM will be a problem as it is low-surface energy material and crosslinked to boot.