Shock, don't let that 746w per horsepower thing confuse you. That is a theoretical number. You have to use the nameplate rating or 430.148.
I doubt the dishwasher has more than 1/4hp motor in it and I bet it is smaller. The 8.7a reflects the 1kw heating element and the timer. The disposal is probably 1/2hp, maybe 3/4.
I agree 430.(A)(1) seems to prohibit it but that conflicts with 210.23(A)(2). I also agree with Steve that this will probably never cause a problem and it is not a danger to the 12ga conductors but the AHJ will have to agree with that too.
The more I read the more confused I get. Simply the wording of the first sentence of 430.53(A) is contradictory.
"Several motors, each not exceeding 1 hp in rating, shall be permitted on a nominal 120-volt branch circuit protected at not over 20 amperes", but a 3/4hp motor is 7.6a.