Levi can confirm if this is correct or not but I believe that you can just walk into a lounge and show the card and you'll get in. As far as Elite statuses like SPG Gold etc. I don't know if the additional card holder will get as well.
Being that it's a business account, it should allow you to limit spending on it. But a word of warning: only split it with people you know and trust. When the second year comes around and all you have is an e-mail address for some guy who you split it with, you can end up getting royally screwed. I had a similar situation with a cell phone plan split amongst a bunch of guys. Bad idea.