Did this "opposing attorney" instruct you to take a witness?
If so, I would assume it's allowed in your state, if not - don't do it.
Never do anything without your lawyers knowledge or instructions.
Personally, I wouldn't recommend it.
That IME is hired by the carrier to give an opinion independent of your treating physicians influence.
He will give an opinion that supports the carriers interest, he has no intention of being fair.
I wouldn't give him anything to use against you - he will probably claim this witness interfered with the exam, the carrier will then deny your claim.
Just go there, be polite, cooperate and get out in the shortest time possible.
Be aware, you're probably being followed and taped from the time you leave your house to the time you arrive at the exam - act accordingly.
Here's some good articles on this topic:
Moderator Responses are based on my personal bias, experience and research - They do not represent the views of the admin nor may be accepted in the legal community, always consult an attorney.