Does Greenplum support dynamic sql?
I cannot tell for sure, but there is a hint in the CREATE FUNCTION documentation:


  langname
  The name of the language that the function is implemented in. May be SQL, C, internal, or the name of a user-defined procedural language. See CREATE LANGUAGE for the procedural languages supported in Greenplum Database. 


In turn, the referenced place says


  The PL/pgSQL language is installed by default in Greenplum Database.


Now the EXECUTE ... USING is a PL/pgSQL feature, so the only question is which PostgreSQL version it comes from.  The documentation points to 8.2 - and this way it looks like you are out of luck.

I've contacted the Greenplum support to get a definitive answer, but never got an answer.

As for working around the lack of that construct, you can obviously concatenate together any SQL string you want and execute it.  Be careful to correctly quote the passed-in values and avoid SQL injection.