Not saying you are immoral here -- just that it does seem to pose a dilemma. I have not had to interview someone for a company that I want to leave. It sounds like it would suck and require some level of internalized rationalization to go through with it.
Two, it's easier to leave a place when you know you've left a project in good hands, instead of knowing things will unravel if you do. Mostly, it's an ethical problem if you sabotage the hiring.
But I'll agree that there is a tension between professionalism and social responsibility. What do I owe to my employer, what do I owe to the local developer community? The next time I interviewed, a guy I had a lot of respect for referred me to a used-car-salesman of a recruiter for a place he was leaving. I did contract-to-hire, walked away from that one. Felt a bit like a meat shield to cover his retreat. I realized all the things I respected him for were past tense, and honor that but stay the hell away from him now.
Is the problem with the company or that the company is no longer a good fit for the interviewer?
Personally, I've been interviewing people to join the company I work for while also on the lookout for changing jobs and I don't feel it's immoral.
I would recommend my current employer in general, but I'm not sure it's still the right place for me.