I can't see how the adapter in the photo on that auction would work with an RGB, but maybe if you order for an RGB he sends you something different to what's pictured... The seller is a member on this forum, so probably a trustworthy guy... Maybe send him a PM and see what he says...
But in my experience, you need at least 11 pins for an RGB laser. R+, R-, G+, G-, B+, B-, X+, X-, Y+,Y- and GND... I also have interlock and DMX connected to ILDA on my RGB's, so I would need 15 pins...
Like I say, I use QM2000.Net's and have never needed to make these adaptors, so maybe there is some clever trick I don't know about, but I can't see a logical way to carry RGB signals down a single Ethernet cable...