No, it's just useless stored information on your computer.
Safe to delete.
quote:
Originally posted by http://www.google.com/search?hl=en&q=define%3Acache
A store for frequently-used data or files. Data can be accessed from a cache more quickly than from its original source.
Contacts are saved on a server (not your PC), and the only way to remove them is in WLM itself.