Well, the UMAX 1220U is supported now. The 1200U was not listed as being supported or unsupported. The Minolta Dimage Dual Scan 3 is supposedly supported by VueScan (Not Open Source, but there are Versions for Mac, Windows & Linux. Free trial version available)
I also use Gentoo. It's a nice distribution, but I learned a lot about linux and the linux kernel during the install. f your not used to Linux/Unix you might want to try something else.