AMD graphics drivers have for some time had a bug that makes rigged mesh clothes in Second life invisible. This has been fixed in the latest 15.7 driver which is now out of beta testing, I updated today and so far all is good. Yay!
Second Life uses Open GL which AMD don't support that well, though fortunately I've never had the problems others struggle with. The biggest visual glitch is with visually overlapping alpha textures which are often displayed the wrong way round.