It looks like init-scripts don't get the environment variables defined for a node, or global environment variables defined in the main Configure Jenkins page, injected. At least for EC2 nodes.
The environment variables are present when running jobs, but not when running init scripts. Even when those environment variables are shown in the "Enviroment Variables" list under "System Information" for a node, an init script that has a line like:
will print an environment that doesn't include them, and shell substitutions won't use them.
In case they were set but not exported I tested with:
but the vars weren't present there either.
This makes it harder to parameterize init scripts.
The environment that was set was: