That is a good strategy, just be casual about it, even for designers not planning to leave it is probably good to have some sort of agreement or understanding around this. Consider establishing these ground rules with your new employer.
I would also say that if you are interviewing at a company in a totally unrelated industry then it would be less risky, but I agree, you never know who you might run into.
If some of the projects are purely stylization projects then I think those should be fine unless your company has a strong reputation for being a trend setter in a realm like fashion, apparel, or soft goods.