TTL RS-232 current limiting
No, you can connect the ATmega directly to the FT232 etc.

In general, a TTL or CMOS level output does not need a current limiting resistor when connected to an equivalent input. Reasons to include a current limiting resistor can be


damage limitation when the output is accidentally connected to ground, power, or another output
damping of oscillations &amp; limiting edge speed, both mainly for relatively long connections (not likely to be needed for the design of average PCBs)