There is a floor rating between units, electrical issues (where is the panel for the other unit) heating systems, plumbing shut offs etc, let alone zoning issues.  

The sellers at my last appointment in Muskegon, Michigan were heating their house with their stove 😳What's the craziest thing you've seen?

If there is one thing that you don't cut corners, it is the heating systems and furnaces.

Let's say you purchase in the winter and find out it is going to take two months for the electric company to approve and re-connect the electric connection to the property to enable basics like heat and water needed for construction (this happened to me).

@Nathan G. had the best idea in my opinion, most landlords don't want legal heat from tenants so a well-written letter citing the codes, etc... is the best route to go.  

I have insulated garage doors for my primary-it is heated-and uninsulated for my rentals.

There is an underground oil tank that is currently used for heating and hot water.

If its been winterized the inspections are going to be a problem, you'll need heat to turn the water back on to look for leaks and then it will all have to be winterized again.Why would they be empty?

I am going to put an offer in on a multifamily in my area but the only problem I came across is that both units are heated with oil.

If you are talking about an older multi-family with heat being one central unit, that's of course something else.