Do the Death Eaters know Snape is with the Order?

[sibel_saya]

No: HPFGUIDX 68338

I don't know if anyone has noticed this or brought it up, but 
something struck me as weird for a long time.

Snape has always been nice to Draco Malfoy and surely he wouldn't be 
as he is a reformed Death Eater, having betrayed Draco's father. So 
why? The only explanation I can come up with is that Malfoy doesn't 
know he's with Dumbledore and he doesn't want to give himself away.

Another thing to support this is in OoP p657 (UK edition) Umbridge 
says, "I expected better, Lucius Malfoy always speaks most highly of 
you!" I'm sure Lucius wouldn't speak very highly of Snape if he knew 
Snape betrayed Voldemort. Voldemort knows the Snape has left as he 
said at the end of GoF but you never know he might be talking about 
someone else. Anything is possible in Harry Potter.

I don't know whether I've missed something glaringly obvious and 
important, and if i have feel free to point it out for me.