[s]No, it is in the default macro API or whatever. You can not use it to cast spells though.
[/s]
I use (and just made this week) a macro to call my non-combat pets. I don't have all the code in front of me but all it basically does is

/e plays Pet Lotto!
/in 2 /script to call random pet

And it works just fine. what were you you doing with /in that broke?

EDIT: well maybe it isn't in the default UI. Now I need to figure out what addon gives it to me because I didn't have anything going that gave it to me on purpose. wowwiki says cosmos but defenatily don't have that. And I can't find a reference on wowace, yet.