Its certainly possible; I know nothing of the zend framework. Objects can be tricky with this; there is nothing in place that says I cannot generate the output via referencing and populated it after the fact (kind of like the way prepared statements work when you bind results and variables to the statement). I can see this especially being the case should the output be something that is used repeatedly for different output.
I can't test this where I am. I wouldn't expect an inclusion to have any impact on the use of error_get_last as that would be linked prior to runtime. Another thing you *could* try is to use the $php_errormsg (with track_errors enabled in ini) as a reference. I don't know if it will work given the nature of the special $php_errormsg variable, but I know for sure it won't work for error_get_last. So you can't get a trace, only a message.
That would be a simple test as:
$err = &$php_errormsg;
$a = 5 / 0;
printf('Last error: %s', $err);
if that shows division by 0 error, than the $php_errormsg can be referenced (normally a variable can be, but this one is a bit on the special side).