This is a bit long, and rather personal, but I wanted to respond in detail:
I have dealt with severe OCD and oneitis at the same time. Absolutely brutal. The general answer is that getting control over your OCD does help substantially with dealing with and avoiding oneitis.
A more specific answer might depend on the type of OCD that you have. As I recall, there are 4 primary types. The type that I deal with personally is often called "the checker". To put it simply, it takes me a certain bit of effort to leave my apartment and feel that I didn't leave the oven on or the water running.
This "effort" used to involve 15-90 minutes of rituals designed to ease my mind of my very real concern that I would make a mistake and thus damage my apartment and possessions in some way. Checking faucets, the oven, door locks over and over (and over) again.
It developed rather suddenly in my early 30s, and realizing that I was literally going crazy was extremely disconcerting. My relationships during this time reflected my constant over-analysis and worrying. Non-spoiler alert: they didn't end well.
18 months ago, I made a determined decision to fix my issues without medication. I relied on something I describe as "certainty of thought." I still check a couple things on the way out of the apt, but only once. And once I decide that, for example, the oven is off...its off. And I do not allow that thought to be challenged by my mind. Now it takes me about 1-2 minutes to leave the apartment. It was a slow process at first to change, but eventually became habitual and easy. The damaged thought patterns are still there below the surface, but I choose to ignore them.
The thing is, I believe that somewhere in the mind of an OCD person is a desire to be a "good person". To succeed, or in my case, protect my assets. Like you said, it helps you succeed at work. It just can spiral out of control. It is paramount to hold on to the good while discarding the excess which only causes problems.
My relationships are certainly better for it. The most important thing that has changed is that when a relationship with a girl goes into that weird, mixed feelings, "I feel like I'm losing her" phase, I just accept it as broken, maybe try to learn a lesson, try to laugh about it, and move on. Rather than going into hyper-analytical mode to try and fix it. And when I meet a new chick, instead of trying to figure out if she wants me or just wants to be friends, I just go for the lay. It never fails.
Best of luck. A lot of people joke about OCD, but having seen it seriously impact my live, I know it is no laughing matter.
