Electrical – Is the water heater installed properly

An Approved location that I'm aware of is like a Floor Drain. Though Ariel is Correct, you would need an Air Gap. So the pipe would have a 1" min Gap to the Drain so that any back flow of water could not touch the exit pipe. The Main issue here is keeping the sewer gases in the system and not outside. This is what the p-Trap is for. Its a water barrier to prevent sewer gases from escaping the system. The Water Heater Drain pan does not typically have water and any p-Trap installed in that line would not have any water in it to fill the p-Trap.

My HVAC system is in the Attic and it sits in a large drain pan so if the AC leaks water will drain out. They plumbed the 3/4" PVC drain to a Soffit vent over a window. The purpose for the over the window was it would be obvious to someone that there was a leak.

Hope that helps.

I have to say, similar to what @Grant said in comments, that an overflow valve is not supposed to have a normal drip. In normal usage your drip/overflow line should be bone dry.

The plumber that tried to tell you that a drip is normal is not to be believed. It is also likely that the plumber was far from professional if they just said that to cover up noting the drip right after the installation.

The pressure relief valve is a safety device designed to keep the hot water tank from exploding if the internal pressure builds up too high due to the heating source failing in an always on state.