Is there a CMDI profile I can use to describe web services?

There are multiple suitable profiles, as described in the CMDI core model for web services (and extended documentation).

See also the following paper:

Windhouwer, M., Broeder, D., & Van Uytvanck, D. (2012). A CMD core model for CLARIN web services. In Proceedings of the workshop on Describing Language Resources with Metadata: Towards Flexibility and Interoperability in the Documentation of Language Resources at LREC 2012 (pp. 41-48).