I don't think it can hurt...
If you link someone from both sites... it will give person you link credit for 1 link only.
In case with different sites... many different sites have the same ip and they rank well... Many large companies have 1 ip for all their local dealers and they rank well for local results.
Example:
http://www.sony.com
http://www.sonystyle.com
http://www.sony.net
http://www.sonypictures.com/
http://www.sonymovies.com/
http://www.playstation.com/
http://www.sony-europe.com/
+ millions official local SONY sites. many of them on the same ip.