Update: Adobe contacted me and told me that the D7100 listing for the Camera Raw 7.4 release candidate was a mistake – they have since removed it from their website.
The latest Adobe Photoshop Camera Raw 7.4 release candidate does have added support for the just released Nikon D7100 DSLR camera. Adobe Lightroom 4.4 release candidate however does not support the D7100 for now. You can use Nikon ViewNX 2.7.4 until Adobe releases their next version.