Please refer to the explanation for workmen under ESI act.As per this those who are drawing Rs.6500 or less are workmen.
So the Medical representative's are to be covered under ESI.you can also refer to the case laws on this.
With respect to the dispensary they can be registered under any dispensary of their locallity.You have to issue the respective form(I am sorry, i cant remember ) to your employees (at their convienient dispensary).
For instance our office is at chennai.But our marketting staffs are enjoying the benefits across all major cities of Tamilnadu.
No matter your Head office is in different area , your employees can very well enjoy this medical treatment benefit at their nearest facilty.
Approach your local office for assistance.
The ESI limit is Gross Wages of Rs. 7500/- per month.
I think that within a state you will get ESI benefit but it becomes difficult to access help from any State other than the State in which ESI is registered.
Although legally it is applicable but practically the arrangemnt you are talking about your office have, it will be difficult to get help and there are a lot of administrative red tapes which will prevent you from getting proper help.
Ofcourse ESI is applicable to all the employees whose salary is not more than 7500. For your M.R. you can provide the form-105 for out station employees & they can avail the medical benifit showing the form-105 across the India. If your M.R. are contineously out of station for a perticular location you can apply for the ESI sub code on the basis of your employees local address. you can provide the employees local address is your local communication address & easily you can allot the ESI sub code for providing the ESI cards for your M.R. Also follow the procedure of out sourcing company, how the are getting the ESI sub code without any office or business premises.