True, but it would require more infrastructure than void fuel to rocket fuel, and being another type of thruster allows you to mess with variables such as the consumption rate, efficiency, and thrust output.
Edit : Also, on my voidblock game, while I did use summoned void fuel into boilers, it is very much not a good power source compared to summoning light oil and turning it into rocket fuel, or using voidium to make nuclear power. Had to use 6 voidwork to summon enough voidfuel for ~8 boilers.