I looked all over the ASUS web pages, and could find no mention of it. Look in the downloadable manuals too, doesn't mention it like the P9X79 manuals do.
However, I see you had a separate thread here and people point to a youtube video that shows its there. I don't have one, so all I can say is what I see on the ASUS web pages/manuals.
http://www.tomshardware.com/forum/302940-30-asus-rampage
This post has conflicting reports. One person says no, another shows BIOS screen shots (which I assume are from the RIVE):
http://ocxtreme.org/forumenus/showthread.php?t=6406&page=2
I have seen other reviews where ppl confuse statements made about the P9X79 + ssd caching with the Rampage IV.
The ASUS ssd caching implementation on the P9X79 and Sabertooth does not appear to have a capacity limit for the cache drive, unlike the Intel at 64 GB. I hope it does, I'd like to get one!
EDIT: I reviewed the YouTube video from the other thread, and it's about the P9X79 and Sabertooth series, not the Rampage. In the video, the Asus guy specifically says "this is one of the motherboards that has it" implying that they have mobos that don't.
I've contact Asus about it, but have not heard back yet. Anyone actually have one of these things and can confirm??
I'm going to contact Asus directly to get a straight answer....