UART LED Driver using MOSFET
The drive voltage refers to the \$V_\mathrm{GS}\$ at which those \$R_\mathrm{DS}\$ values are reported. The maximum \$R_\mathrm{DS}\$ was measured with \$V_\mathrm{GS}\$ = 2.75 V, and the minimum \$R_\mathrm{DS}\$ was measured with \$V_\mathrm{GS}\$ = 5 V. Your understanding of the other parameters is correct.

Your circuit will probably work, but you may encounter problems at higher baud rates. The MOSFET has a gate capacitance \$C_\mathrm{GS}\$ which will distort the edges of your serial signal. This value is referred to as \$C_\mathrm{iss}\$ in the datasheet, with a maximum value of 50 pF.