Yes you can use exchange on any internet plan verizon offers. I use it myself and it works great. Push works fine.
Just make sure you don't tell the verizon employee you are going to use exchange (unless you have a nice one and they actually suggest using the lower one, like mine did).
There is absolutely nothing different between the regular 29.99 and corp 45.99 data plans.
I did see an article way back when I was first looking into the eris that one of the senior VP's of verizon stated that the 45.99 plan is intended for business accounts. IE...if your business is paying for the phone, they want you on the 45.99 but if you are an individual/family then no matter what you should be on the 29.99 plan. This however, has not gone into practice. Store employees will hear exchange and force you on the 45.99 plan. SO DON'T MENTION IT!