I've had experience with ball pythons taken from the wild that didn't adapt well. they wanted to eat gerbils and only gerbils. so had to feed them gerbils which weren't always available. you are talking about a domestic animal though so it would be a bit different. out of curiousity I looked into the guinea pigs a bit. looking for things that might affect importation. good things are of course that they are easy to transport. but some things to look into further that could be a problem with importation on a practical level....
under hygiene
"guinea pigs are notorious for there susceptability to many diseases"
www.metafro.be/leisa/1989/5-1-22.pdf
also....
"They do not respond well to sudden changes in diet; they may stop eating and starve rather than accepting new food types.[52"
http://en.wikipedia.org/wiki/Guinea_pig of course guinea pigs managed to make it all over the world on ships as novelty pets hundreds of years ago so I can't imagine that importing them in modern times can't be done.
may I ask why the cui and not rabbits? alot of energy could be spent to get the cui stock and most people from what I read think they are far inferior to rabbits as meat animals. or are you wanting to have them both for the'rabbits eat guinea pig poop' thing?