That is an awesome question!!!
My experience tells me "No". I have been an administrator for 6 years with the PDM workgroup
and this was not an option, but you are referencing Enterprise PDM and while I have limited
experience with it I still haven't seen that ability. I know in both that permissions can be set
on folders for RW access. I think you are better off if you are able to, move the drawings to a
seperate folder and allow RO access to it for this group.
I have the same opinion that you can not accomplish that but you can create automatically pdf files from drawings on some action let say released. After that you can move these files in a state where a group or some users can see.
You can set different read permitions if you set 3D files to a different Workflow. Be sure to name the same transition names to be able to cascate the change state operation to parts and assemblies when you change drawing states.