The returned "result identifier" can not be used for retrieving anything but the sesam_affected_rows(); it is only returned for symmetry with the sesam_query() function.
Note that sesam_query() can handle both "immediate" and "select-type" queries. Use sesam_execimm() only if you know beforehand what type of statement will be executed. An attempt to use SELECT type queries with sesam_execimm() will return $err["sqlstate"] == "42SBW".