When you appeal the denied offer do you go to Tax Court? Can an accountant still represent the taxpayer at Appeals?

No, when the Offer is denied and you file your appeal it will go to an Appeals Officer in the Independent Office of Appeals. This is still an administrative procedure, so any representative who can be on a Form 2848 can represent the taxpayer at the Appeal (ie. Enrolled Agent, CPA or Attorney). If the offer was originally filed through a Collection Due Process Hearing, and you cannot come to an agreement with the appeals officer, you have a right to seek judicial review in U.S. Tax Court if the IRS abused its discretion.