Why do some dNTP mixes contain dTTP and others TTP?
Thymine is normally found as a deoxyribose. Thus, TTP and dTTP are essentially the same thing. Both types of mixes can be used in PCR reactions
Can dU-containing DNA produced by amplification with dUTP be cut by restriction enzymes?
You will need to confirm with the manufacturer of the restriction enzyme you are using to find out whether or not it can recognize dUTP-containing DNA.