UHS and UDMA are two different but related standards, and support for UHS is not necessarily a requirement for "using" cards faster than 30mb/s. UHS cards are still UDMA compatible, and will revert to the UDMA interface if UHS is not supported.
As for whether using a speed faster than 30mb/s will help, probably not with an SD card. I think the maximum write speed in SD/SDHC cards is 30mb/s (Class 10), while the read speed can be faster than that on the same interface. You only gain the improved write speed benefit if your interface is UHS compatible.
As a side note, if you use Compact Flash (CF) cards, you can definitely get very fast speeds with UDMA interfaces. I believe UDMA-6 has reached 90mb/s or around there, and UDMA-7 has reached 150mb/s (with Lexar 1000x cards). The SD/SDHC standard has kind of stagnated, and it seems its been stuck at Class 10 (30mb/s) for quite a number of years. The UHS standard does not seem to have caught on as well as some expected as well, and the SDXC standard, which will supposedly support up to 300mb/s, has not materialized all that well either. Some SDXC cards exist at speeds over 100mb/s, and a few cameras (mostly compacts, I'm not aware of many DSLR's) have supported it since the beginning of 2011.