Question

Also other such Pokemon, like Chansey.

Answer 1

Yes but no. The pokemon will still go into the evolution screen, but it will stop, and the pokemon won't evolve. After etting the national dex, they will.

http://www.serebii.net/red_green/evolution.shtml

Comments

This was fixed in new generations though, so don't worry about this now. It's Dex number will just be question marks.