I think that there is already a *great* solution for provisioning Eclipse Environments, including the Eclipse Platform SDK: Oomph. It seems that the power of the tool is still not well understood. Using the instructions on the wiki , it is literally a few clicks to set up an Eclipse SDK including *all* (not only EGit/JGit) dependencies to build and develop the tools. For instance, EMF Tools and E4 Tools are installed when doing platform UI development. Note that these tools will not be installed if you don't include the Platform UI project, so even a minimal set of dependent tools is installed.
Moreover, it is straightforward to define custom configurations for Products and Platforms. You could create and publish a SDK Product configuration that includes EGit next to the existing SDK. Also, for the more advanced user, you could even use user-configuration to install some features in every Eclipse instance you install with Oomph.
IMHO, the Oomph configurations take care of 'the thooling we rely on', without polluting the SDK product or development environments of others.