From what I can see, it looks like it depends on exactly what you have.
The basic EM18 seems to be a square 32mm by 32mm module with 9 pins, one of which is a serial output pin ("TX"). Some sites call this output "RS232" but it is evident from the way these modules get used that the voltage on the TX pin is not at RS232 levels, but is determined by the EM18 supply voltage - usually specified as being from +4.5V to +5.5V, although I did see one lookalike where it said that it could operate down to +3.3V. The TX line from a module like that could connect directly to a MCU pin, (subject to 5V tolerance on the MCU pin if say the EM18 was running on 5V and the MCU on 3.3V).
However, to confuse things a bit, you can also get the basic modules mounted on small PCBs with various additional components, in some cases including a MAX232-like voltage level converter. You would not connect the output of a chip like that directly to a MCU pin.