I have used the Green Slime compressor with the power plugs in my 2012 Touareg TDI with no problems. As to fire risk each power receptacle is fused to protect the wire.
I have not used the compressor to blow up the spare, but to adjust the air all the way around.
The fire risk is minimal or non-existent.
I got my Green Slime compressor at a yard sale for $0.25 so it wad a bargain.
My TDI does have the compressor in back, but when traveling towing a trailer and a full back compartment it is hard to get to.
I have used it with my 2012 Touareg and my 2016 Town & Country van with no problems.
Most accessories that have a cigarette plug draw less current than the plug in the car is good for and are also fused within the plug as well.
It may take longer to inflate the spare in the Touareg, but it should work OK