Do companies ever initiate contact in b-school?

I actually faced this exact issue. One of the companies that sought me out was a consulting company that did exactly what I had just done before. I had made it clear that I was going to try something new for the summer, but a partner insisted that he wanted to talk to me in what ended up turning out to be a pseudo interview / sell conversation.

What I did was follow up in two ways - first I called the HR person who had been in touch with me and said pretty much the following: "I enjoyed speaking with X partner and really have enjoyed all my interactions with Y company. That being said I know some fellow classmates who are really interested in trying out consulting this summer and don't want to potentially hold up any opportunities for them. I am potentially interested in full time opportunities in the fall, but want to pursue something totally new this summer."

The HR person really appreciated that and followed up with an email a few weeks later telling me that if I changed my mind, they'd love to talk with me in the fall. I also emailed the partner with a similar message thanking them and looking forward to talk to them later.

Incidentally, I followed the same approach in off-campus recruiting in the spring. There was one opportunity that I turned down mid-process after I had gotten two offers. I basically spoke with the HR person there too and explained that I had gotten two offers and I planned on taking one and wanted to step aside. She also was very appreciative and told me to follow up with her in the Fall. Incidentally, the other Kellogg student who was interviewing with me (we drove to interviews together) ended up getting the position for the summer.

Basic message is this: if you are honest with recruiters throughout the process, genuine, and appreciative then you generally won't burn bridges. Recruiters appreciate honesty greatly and being dealt with in good faith. So long as you follow those principles then you'll be fine.