We have OpC and Omni on the same server with no issue and therefore are unable to comment.
Suggest you open a call with HP against your maintenance contract.
What do you mean with "omni is not responding properly"?
omni can't connect?
omni connect but abort the connection?
what kind of errors do you get in debug.log?
what happen when you have omni running and then you start OpC?
All servers we have, have them running with DP and OpC and never found this problem.