Can I use two 10 ohm 5 watt resistors instead of one 5 ohm 10 watt resistor?
Yes, that would be fine.

The goal is to draw 1A from the 5V bus as a "dummy load". Each of your 10&Omega; resistors will draw 0.5A, dissipating 2.5W in the process. The two of them in parallel constitute the desired load.