In order to remain current, each Eclipse release targets reasonably current versions of the underlying operating environments.
The Eclipse GMF Tooling project depends upon on the Platform and other projects, which are mostly "pure" Java. The 3.8 release of the Eclipse Platform Project is written and compiled against and targeted to run on Java SE 5 and Java SE 6 VMs. GMF Tooling will target the same Java version(s).
Eclipse Platform SDK 3.8 will be tested and validated on a number of reference platforms. GMF Tooling is expected to be platform-independent, but will be tested and validated against a subset of those listed for the platform.