Although proper procedure would be to have a cert created for the host name & FQDN of the SCCM OOB, as long as the domain name stayed the same you should be fine. I have that same scenario running in my development environments. Just export it with the private key and use it within "Site Database"-> "Site Manager" -> Site server Name -> "Site Settings" -> "Component Configuration" -> "Out of Band Management" configuration setting as normal.
Thanks for the input. After much thought, I found it wouldn't be a problem to 'lock' it on one server name. I've been lucky enough to get my hands on a new HP system which I can use for the OOB service point. However, it is good to know that if I decide to move things around I shouldn't be penalized.