There seem to be no static errors specified for the signature provided for main, and the runtime semantics don't seem to make it clear that as a result the invocation needs to do a dynamic type check. In practice, the VM at least seems to do so.
This program:

void main(int x) {
  x.isEven;
}

produces the following runtime error when run:

Unhandled exception:
type 'List<String>' is not a subtype of type 'int' of 'x'
#0      _startIsolate.<anonymous closure> (dart:isolate-patch/isolate_patch.dart:299:32)
#1      _RawReceivePortImpl._handleMessage (dart:isolate-patch/isolate_patch.dart:168:12)

This seems like it needs clarification in the spec, and possibly tests.