I'm not aware of racks that come in "widths" as far as mounting goes. Most bikes (that you'd put a rack on) have either 130mm or 135mm dropout spacing, so rack makers assume you can flex the rack struts enough to accommodate a few mm's more or less.
Looking at pic of the Vita online, it seems to me that the rack mount bosses at the dropout are molded as part of the seatstay socket, meaning you have to mount the rack not only outboard of the dropouts, but also outboard the seatstay, which would make it pretty wide.
I'd suggest either 1)try spreading your current rack out to fit (use a little muscle. If you break it, well, you were buying a new rack anyway ;-), or 2) if there is room inside the seatstay and clearance from the cassette gears, try mounting the rack inside the dropout, rather than outside. Using button-head bolts, rather than socket head, might help with clearance there, too.
I have 2 Topeak racks that I've mounted to pretty wide MTB frames with no problem, but I'm sure a PB or Delta rack could be made to fit as well.
Just my 2c.

-Pete