I know there is controversy regarding use of ssri/snri in bipolar 2 but if ocd is highly prevalent how can the use of one be avoided.cbt is also used?

Yes, CBT for sure: Cbt is a very well-researched and useful part of treatment for ocd. Other-than-ssri medications may be used, and you may still be able to use ssri's. However, you need to work with a skilled psychiatrist who keeps up with the most recent psychopharmacological treatments. http://ocd.stanford.edu/treatment/pharma.html.

Antimanic: If benefits out weigh risk an antidepressant can be prescribed for a patient with bipolar disorder and ocd. An anti manic medication needs to be prescribed to reduce the risk of manic.