So, just to clarify, yes, the Ultra will "accept" an standard 1911 mag, including GI 7-rounders. However, they will stick out the bottom.
Standard Officer's Mags hold 6, but just like you can now get a flush-fitting 8-rounder for full-frame guns, you can also get flush fitting 7-rounders for guns with Officer-sized grips. *These* are the 7-rounders that Kimber is talking about.
I will second the recommendation for Wilson mags. I bought the stainless 7-round Officer's mags from Kimber for my Ultra CDP and was unimpressed. The Wilson mags I replaced them with have been flawless.