Yes, a humidifier can add a slight amount of heat to a house, but less humid air is generally cooler air because it does not retain heat as well.

If it's 75 F and 80% RH indoors and outdoors, 11.8% of people would find that "too warm," according to the ASHRAE 55-2004 comfort standard.

DEhumidifiers add about 1600 Btu/pint. An average house with 400 Btu/h-F of conductance and 200 cfm of air leakage would be 79 F with 65% RH with a dehumidifier removing 1 pint of water per hour, and 27.3% would find that "too warm."

OTOH, an AC using the same amount of electricity and removing 1500 Btu/h of heat and 1.5 lb/h of water would leave the house 71.3 F and 82% RH indoors, which would only be "too warm" for 5.1%...

Nick