Can fibre patch leads pass through the brush?

Yes. Fibre patch leads can pass through the brush, just as copper patch leads can.

The brush presents only light resistance and is not intended to clamp the cable.

What matters is the route on either side: a perfectly harmless passage through the bristles can still be followed by an ungainly bend if the cable is pulled immediately around an obstruction.

Respect the bend-radius requirement of the particular fibre lead and the brush itself is not the troublesome part of the journey.