We have this situation in our building. First of all, the building is served by propane for heat and hot water. No meters of any kind for the propane. There is a 2000 gallon tank on the property that serves the building. We get the bill from the propane company when the tank is filled. The previous owner set up a system of charging a flat rate to each apartment each month for the propane service. Conceptually it's like being put on a budget system by the gas company. And legally it's considered part of their rent since the amount is fixed and disclosed upfront.
Second, we have individual electric meters in the building, but the city won't read them. There is one meter on the outside of the building that they read every month and send us the bill (along with water and sewer). There are 15 meters in the basement (14 apartments and one for the house). I read those meters every month on the same day that our outside meter gets read. I then produce a utility statement for each tenant that has their propane budget amount and their electric meter reading amount. The previous owner had a formula he used to calculate the electric usage amount for each apartment based on their meter reading.
I had this same concern about being considered a "utility provider" so I met with my attorney to discuss it and get his opinion if doing this is okay. By the way, whether or not you make a profit is immaterial. You can be "in the business" if you make a profit or not, so that argument above doesn't matter. If it's okay to resell something at a loss, then it's also okay to resell it at a profit.
In my state, this issue is not addressed in landlord-tenant law. There is no prohibition against re-selling any services other than sewer. It specifically says you cannot re-bill sewer services, because they are never metered. There are also a bunch of rules around water services because as everyone knows they are frequently a subject of dispute between landlords and tenants. However, nothing regarding gas or electric service.
In Nebraska, municipalities often run their own electric utility services, and as such have pretty much complete authority to set the rules of how utilities operate within their jurisdiction. Since the city refuses to read the meters inside my building, they are thereby granting me approval to read the meters and bill the tenants. The one rule they have to follow is that they have to provide service in the city and the rates have to be "reasonable" I also have to do those two things. I have to provide service (duh, that's what landlords have to do anyway) and I have to charge a reasonable rate. This is also no different than apartment complexes making deals with cable TV companies to provide service to the building and then re-selling that service to the tenants either at a profit or a loss. Cable TV is also a regulated industry.
Bottom line is that just like everything else in real estate, local laws vary considerably. Utilities are very local and all the rules are set locally. Check with your attorney to find out what's legal in your area and be wary of people on message boards spewing about how something is absolutely this or definitely that.