It is odd to say "About one worker". It would be normal to say "About 100 workers", to mean between 90 and 110 (or more, or less, in context)
If you mean a small but non-specific number use "a few":
The company employs a few contract workers.
It would be fine to say "about 1 metre" which I would understand to be in the range 0.9—1.1 m (or perhaps a smaller or larger range, in context). But I would not call 2m to be "about 1m". Similarly, I would not call "2 workers" to be "about 1 worker". This makes "about 1 worker" a rather odd expression.
Similarly "about fifty to a hundred workers" is fine, but "about one or two" is odd. Just use "a few" in this situation.