By backwards compatible they mean Genesis, G2 & G3 will work by autofit (to a certain degree, I can't get High healed shoes/boots to work and I can't get V4 or earlier to work via autofit, I haven't had a play trying other things) and G3 base UV skins work on G8 but not all. So if you have the texture transformer you could probably get Dawn skins to G3 to use on G8 (or G3 back to use on Dawn) but I don't know about clothing.
This is a list that someone came up with, there could be other skins that work/don't work that they didn't have:
Compatible Uvs: G3F Base Female, Arabella 7, Dandelion, Eva 7, Gia 7, Karen 7, Lilith 7, Mei Lin 7, Monique 7, Olympia 7, Victoria 7
Uncompatible UVs: Aiko 7, Bethany 7, Demonara, Genevieve 7, Girl 7, Kalea 7, Rune 7, Sunny 7, Teen Josie 7, Tween Julie 7