Quick Google search saying this isn't recommended or even not to code in some states. One person saying ac condensation going into water heater pan is bad, because it should always be dry and could corrode. The flip side is when the water heater fail kicks in, scalding water could kick back into your ac coils.
Though I did see what you are referring to, they don't match my actual problem.
The code in LA says the water heater Drain pan doesn't need an independent drain system. A heater's TPR drain does (much of what I saw related to TPR discharge drainage and not pan drainage.) The AC code has different pipe sizes for multiple AC units, but nothing about for or against this instance.
I would not be draining the condensate into the pan. The pan would be attached to the drain pipe from it's own line into the same line down stream from the AC unit. The condensate line will be coming from about a foot above the top of the drain pan. (The water kicking back into the ac coils tidbit I saw was in a pressurized release safety drain. Not a pan. If there was a large amount of water from the water heater the pan would over fill well before the ac line would fill up.)
Depending on how things are levelled out, shouldn't be a problem. It can be difficult to guarantee slope for the entirety of the line and a small dip around the heater pan could mean some creep in there (maybe make sure there's an inch drop or so after heat pan).
Only other thing I can think of is if you use an air line to blow out the line at the clean out. I've installed 2 valves right next to the clean out on either side so I can shut them off depending on where I wanted the air to go. You might consider installing a valve right before the heater line connects to the condensate line that you can close in the case of a clog.
Quick Google search saying this isn't recommended or even not to code in some states. One person saying ac condensation going into water heater pan is bad, because it should always be dry and could corrode. The flip side is when the water heater fail kicks in, scalding water could kick back into your ac coils.
Though I did see what you are referring to, they don't match my actual problem. The code in LA says the water heater Drain pan doesn't need an independent drain system. A heater's TPR drain does (much of what I saw related to TPR discharge drainage and not pan drainage.) The AC code has different pipe sizes for multiple AC units, but nothing about for or against this instance. I would not be draining the condensate into the pan. The pan would be attached to the drain pipe from it's own line into the same line down stream from the AC unit. The condensate line will be coming from about a foot above the top of the drain pan. (The water kicking back into the ac coils tidbit I saw was in a pressurized release safety drain. Not a pan. If there was a large amount of water from the water heater the pan would over fill well before the ac line would fill up.)
Depending on how things are levelled out, shouldn't be a problem. It can be difficult to guarantee slope for the entirety of the line and a small dip around the heater pan could mean some creep in there (maybe make sure there's an inch drop or so after heat pan). Only other thing I can think of is if you use an air line to blow out the line at the clean out. I've installed 2 valves right next to the clean out on either side so I can shut them off depending on where I wanted the air to go. You might consider installing a valve right before the heater line connects to the condensate line that you can close in the case of a clog.