Is it within code to tap into an A/C disconnect box (240v) or hot tub disconnect (240v) and add a 120v GFCI outlet?

I know it can be done, but there may be potential risks that I am not aware of. It's not worth doing something stupid and putting my family at an unnecessary fire risk. I can keep running an extension cord outside when I need the power.

If it can be done within code, I can provide further details on the two circuits if it is dependent on certain factors.

You can buy disconnects with an integral GFCI, but the case has to be open for it to be used.
This is typically done as a convience to the AC service person.

Think about it, the 120 V receptacle is rated for 15-20 A. The disconnect can have a 30 A fuse. The outlet is not fused correctly unless it has a separate circuit.

Your best bet might be a box with a GFCI receptacle that can withstand a plug being connected and it raining outside.

You can buy disconnects with an integral GFCI, but the case has to be open for it to be used.
This is typically done as a convience to the AC service person.

Think about it, the 120 V recepticle is rated for 15-20 A. The disconnect can have a 30 A fuse. The outlet is not fused correctly unless it has a separate circuit.

Your best bet might be a box with a GFCI receptacle that can withstand a plug being connected and it raining outside.
If I was to do this, I would add a separate box with a GFI receptacle.

I didn't think about the 30 amp breaker that controls the A/C circuit, it's a very good point. I can add a breaker in my main panel outside and run it in conduit, but that would require 50 additional feet of wire vs. a couple feet of wire and conduit if I tap into the A/C disconnect box.

Another thing to consider is the hot tub already is supposed to be GFI protected. Aside from the fact that the breaker feeding the tub is rated for 30-50Amp as a #10-#6AWG wire. You are looking at hooking up a receptacle at 15Amp using a minimum of a #14AWG as well as doubling up on your GFI protection. Also, legally you are taking a chance in the rare case you had a fire. Insurance might not cover you if it is not done to code. Insurance companies are beginning to be very anal in this day and age. They are looking for any reason NOT to cover you.

The wires for the new GFCI, I believe can be fished through the, hopefully, existing conduit.
You did leave a fish line in there the first time, didn't you?

Could add 2 circuits to side, or remove and install 4 circuit panel. Is it for convience or does it have a purpose? Some breakers allow a 2 240 volt circuits on 2 poles or 1 240 and 2 120 breaker protection on 2 poles.