Good question, most whole house dehus are able to discharge dry air into ducts with .4" WG pressure. Some are rated for upto .7"WG, but dehumidification declines. Best to setup a relay to interupt the dehumidisat circuit of the dehu when the a/c is running. Normally, no dehumidification is require when the a/c is cooling.
It is also recommended by most to have a dedicated return from the open space of the home to the dehumidifier. The supply from the dehu is routed to the a/c supply. A backdraft damper in the dehu supply stops backflow from the a/c to the dehu.
I work for the mfg. of Ultra-Aire/Santa Fe and several brands of dehus.
Bear Rules: Keep our home <50% RH summer, controls mites/mold and very comfortable.
Provide 60-100 cfm of fresh air when occupied to purge indoor pollutants and keep window dry during cold weather. T-stat setup/setback +8 hrs. saves energy
Use +Merv 10 air filter. -Don't forget the "Golden Rule"