Yes, at least sometimes.
In the 2nd episode of the 2nd season of the British TV show Scrapheap Challenge the challenge was to build a cannon. They tested the cannons in a DERA facility where "real" cannons are tested, and the test was supervised and lead by DERA personal.
When firing the second time, the host of the show asked the DERA person that was in charge (identified only as Maj. Reid):
Can you just explain why, when you are doing your countdown, you miss out number five?
To which he replies:
[W]e don't say number five because it sounds too much like fire, and if they missed a couple of numbers on the way and hear the first bit of it five, they could press the button before we are ready for them.
The entire episode can be seen in this YouTube video, and the answer quoted appears at 36:36 in the video.
This doesn't show that it's used in all parts of all English speaking militaries, it does show that at least one English speaking defence organization uses this.