Most probably what's happening is your brush has quite a transparent look, you won't see this in your renderView per se, since it's comped on black (to check this click on the 'display alpha' button, if it appears dark and grey, your brush has a lot of transparency).
You can solve this by selecting your stroke from the outliner--> attribute editor --> click on the brush tab ->> shading --> you should see your transparancy there.. most probably it's close to white, just push it back towards the blacks instead.
About the particles, if they are not showing up in the Maya Hardware renderview, I think you'll have to resort to using the Hardware Render Buffer instead. I know at least in later versions of Maya particles do show up in the Maya Hardware renderview. However do check your alpha channel again though, maybe it's rendering them out as black?