Should I consult with an attorney even if one is not allowed at my academic misconduct disciplinary hearing?

Yes. The question you have to ask yourself, the answer to that question is, "Is something at stake?" If something is at stake then you need to have an attorney. An experienced attorney advisor in academic disciplinary matters can advise you through the process, can do everything to try to ensure a fair process, and can work towards obtaining a favorable outcome. Regrettably, you cannot depend on the school to be cognizant of your rights and interests through the process. You're not even necessarily afforded the basic right of being presumed innocent until proven otherwise.

It depends on the school in question but you cannot expect the school to do the right thing is what it comes down to. An experienced attorney advisor can help in various capacities both in terms of providing guidance, input regarding a given case, letting you know how to best prepare a defense regarding the academic misconduct allegations. They can help in various capacities regardless of the school's policies regarding their direct involvement in a given case or not and they should be involved from the start of the process.