Are there any known issues if WSUS is installed on OWA Server?
Personally, I wouldn’t install WSUS on OWA or any Exchange Server. But, it is totally supported configuration. Note that WSUS will be installed on a new site – “WSUS Administration” site on TCP PORT 8530 and SSL 8531.
OWA by default will be installed on Default Web Site (on TCP PORT 80 and SSL 443) which can have Secure Sockets Layer (SSL) encryption to provide the secure method for accessing OWA. By enabling SSL on the Exchange Server virtual directory, the URL used to access will change from HTTP:// to HTTPS://
In that case, ClientWebService & Selfupdate virtual directories which are in Default Web Site have to be excluded from SSL encryption or else Selfupdate will not work.