OPS Center 7.5

Opscentre compability is documented in the 

NetBackup (tm) 7.x Operating System Compatibility List

http://www.symantec.com/docs/TECH76648 - Page 71

The answer is yes.

I would recommend getting the 6.5.6 domain upgraded ASAP because 6.5 has been out of support for almost 2 years. Lates version of Netbackup is 7.6.0.2 as time of writing. Lates version of 7.5 is 7.5.0.6

Support for NBU 6.5 has been removed in  OpsCentre 7.6.0.2

from page number 197 in Opscenter admin guide.

Select the appropriate master server version
manually from the drop-down list. You can
select from the following versions:
■ 6.0.x
■ 6.5.x
■ 7.0.x
■ 7.1.x
■ 7.5.x
■ 7.6.x
Note: OpsCenter 7.6 is the last version to
support NetBackup 6.x. You will not be able
to monitor, manage, or generate reports for
NetBackup 6.x master servers in future
OpsCenter releases.