R "capabilities" on a cluster node

The double '//' is harmless. What you are failing at is that your 
R-build-host has the system X11 runtime libraries (libSM.so.6 and
friends) while your execution hosts don't have them, and R_X11.so 
depends on the system X11 libraries which R cannot find on the execution 
hosts.

So - ask your grid engine administrator to install the X11 runtime
libraries on the grid nodes, or ask him/her to build a special version 
of R which doesn't depend on X11. (the former is the recommended 
approach, but your admins may think the latter suit their policies).

Yes, pdf/ps are always available. (they are just save-to-file devices 
using R's own pdf/ps writing code).

The png/jpeg situation are similar to but separate from X11. On the R
build host, you need both the development headers (libpng-devel,
libjpeg-devel, libX11-devel & other libX*-devel packages for redhat
systems) as well as the runtime libraries (libpng, libjpeg, libX*) to 
build R with each of the support for these 3. On the execution hosts,
you need just the runtime libraries.

The reason why you are missing jpeg/png is probably because your build 
host doesn't have the headers. (it is relatively rare not to have
jpeg/png runtime, but the headers are normally not installed).

We (used to?) have a similiar situation on our sun grid - my desktop R 
can do png but our cluster grid R cannot. (ghostscript and a few other 
software can convert ps/pdf to png so it is not a big loss, just a minor
inconvenience).