Absolutely. You need to ensure that the water heater is replaced to code. You need to make sure it is flued, gas piped, or wired correctly. It may cost a few more dollars, but the peace of mind knowing that the installation was done correctly is priceless.
Yes, a hot water tank is a potentially dangerous part of any household system if installed improperly. A permit is required for safety - and Licensed Professionals are the only ones who can obtain such a permit in Ohio. This is important for the safety of of the property, and also for insurance reasons. A building department inspection insures that the equipment is installed to state code, and a Licensed Professional is responsible for the work. This varies by state, so always check with the building department of your own locality.