If your looking for just camo raw goods, your not likely to find much more than heavy nylon and fleece.
Silnylon, to my knowledge, isnt made in camo - though Im not sure why it couldnt be. You can get camo taffeta which you could probably seal with thinned silicone.
As for WHY someone might want camo items for sport backpacking - *I* use a good amount of camo or earth toned colored items because I like being "stealth" and because like the increased wilflife viewing opportunities, and because I DESPISE seeing people running around in bright primary and secondary colors looking like traffic cones in the woods. It ruins the illusion of solitude to look across the valley and see a long train of NEON glaring at you.
If your doing a more risky activity than backpacking, like say, mountaineering, by all means wear something visible, but backpacking just isnt enough of a threat to live in fear of "not being seen".