It is available in all contexts. This file is used to make symlinks in the contexts and commands directories. All MISC values are passed unmodified as environment variables. One can mistreat rstartd in any number of ways, resulting in anything from stupid behavior to core dumps. Other than by explicitly running programs I don't think it can write or delete any files, but there's no guarantee of that.
Error handling is OK to weak.
In particular, no attempt is made to properly report errors on the exec itself. This is a trivial example of an incompatibility that rstart can hide.