I'm pretty positive you can. Meowth implied that you can't, but I think that was just phrasing that he used. I think that if you were to assign the "shiny" stats to your R/B/Y monsters and trade them to your (still unreleased) G/S game, they would be shiny. In order for that not to be the case, the game would either have to change the stats on the fly or set a bit that means "don't make shiny". Setting the bit would be prohibitive, because this scenario could ensue:
Gold: catch shiny Gyrados
Send to Blue
Not shiny on Blue (obviosly)
Send to Gold
Now marked as not shiny.
That's pretty lame, so I'm betting you could. If you can, you need to modify the genes of your monster. There are eight possible gene sets for shiny monsters that we know of (probably in total): All have a gene value of A (10 in decimal) for Defense, Speed, and Special. Here are the possible gene sets that yield shinies:
XX1X 1010 1010 1010
= 2 A A A
So codes for strong shinies in Red/Blue/Yellow (they will NOT be shiny in Red/Blue/Yellow, they will ONLY be shiny in metallics IF the shiny numbers are kept the same [very likely] and IF you can import a monster to the metallics and have it stay shiny [likely]):
When you pop these over, they should be shiny. Meowth, if you know different, correct me.
We'll know for sure whenever it ships in the US...