Yes, cure#1 can work in a liquid marinade. Think about Pop's brine for ham, bacon or brining to make corned beef. Same principle of a salty liquid.
No, you do not use the same 1/4 tsp per pound. In Summer Sausage, all of the Cure gets mixed in with the meat. In a marinade or brine, the meat soaks up the marinade until the salinity level in the meat matches the salinity level in the marinade. Therefore it will not absorb all the liquid.
Martin (AKA DigginDog Farm) has a cure calculator that I believe will handle brining. I would consult the calculator as well as Pop's brine recipe to begin with. You will have to take into account the salt levels in the marinade ingredients also.