On a day of September, I was waiting for an Air Canada flight which was significantly delayed in terminal B. Usually I stay at the United Club. But that day I got three hours and do not have any carry-on other than my briefcase. So I took a small adventure: visit the Lufthansa lounge in terminal E. I chose not to exit to the landside and walk through the central garage or take shuttle, but remained airside to tour the whole terminals B, C, D and E. It took me 30+ minutes and got me very exhausted. The Lufthansa lounge receptionist did not even recognize my BP so I guessed AC guests seldom visited there (understandably). The food there was no better than the United Club but at least the beer was much better. The worse part was I had to walk another 30 minutes to AC terminals.

TLDR: yes, terminals B and E are connected airside, and no, it might not be a good idea to walk through it.