Is EXPTYPE_INTEGER long enough for a pointer

is it safe to return ret=pointers (as RETURN_INTEGER) to be taken back as params[x].GetInt()

or is the ExpType_Integer to short?

Look at the definitions in the header file. It's an __int64, so in theory it can hold two pointers in a 32-bit system, but you really shouldn't do that. Pointers have no meaning whatsoever in events and therefore should not be involved in the event engine at all.