However, if the customer has total control over the escrow account then I would say that it would not be subject.
If that's the case then RESPA would not apply. However in order for the borrower to have total control they must be able transact on the account anytime they wish. You would have no say as to when they made deposits or made withdrawals or in what amounts.
If you control any of that, by any type of an agreement, then they do not have total control and RESPA would apply.