Unfortunately, installers are not electricians and will not assume liability for installing the disconnect.
Nothing special about a disconnect, don't let the terminology scare you. This is also known as a "service switch". It is just a light switch to cut power to the air handler for when repairs/maintenance is needed. If you interupt the two hot terminals with a switch, it will kill power but, the absence of a neutral makes me think that this is not the circuit that is powering the air handler. As far as needing an outlet, I don't know why they are requiring one but, it will require a neutral.