It's a while since I used the ATMs in the airport so I can't be more specific. I know there are a few ATMs of different banks should your card not work with one e.g. I had trouble with Banco Bradesco there even though it's my ATM of choice normally.
I can't help much wrt the Intercontinental as I've never stayed there. Too far out in the sticks in São Conrado.

Others here might chime in it with what's available but I'd imagine it's not that covenient for shops and banks. As well as the local banks there are HSBC and Citibank (less so) ATMs in Ipanema and Copa. BTW there was also a fairly recent thread about GIG hotel shuttle and taxi options.
http://www.flyertalk.com/forum/showthread.php?t=776608