Cerulean's probably not the only place you gotta go to catch those things, but sure. I didn't get to pass through Cerulean myself anyway- took the shortcut instead. I know you two are probably wanna go to Mt. Moon eventually- or at least, Ray will.

[He smirks.]

Y'know, because of all the alien Pokemon there.

Experiment to your hearts' content on the slimeball, guys. I won't miss him, promise.