CA generated SHA2 certificates have been supported since WLC code 7.0.250.
http://www.cisco.com/c/en/us/td/docs/wireless/controller/7-6/configuration-guide/b_cg76/b_cg76_chapter_010111.html
The ability for a WLC to generate a SHA2 Self Signed Certificate was introduced in 8.0.140.0, 8.2.121.0 and 8.3.102 via the following enhancement bug:
CSCuz47863 SHA256 self-signed cert for WLC web admin
