Actually depends on how you specify how you're connected (e.g. I didn't need an email to connect with Sabre- I selected 'We had done business' and selected my Freelance company that any trades here would fall under).
Also, people who go on connection sprees (esp without customising their intro message) get listed as potential abusers and have to enter an email to prove they know the person they're trying to connect with. So bear that in mind if you're adding lots of contacts.