Yes, you can.

But, charging gel batteries with a flooded lead-acid charger is risky.

Why?

Gel batteries like to be charged slow and low.

A battery with a battery charging sitting on top of it
You can use regular chargers with gel batteries, but it’s very risky
So, when charging a gel battery with a lead-acid charger, you must be extra cautious.

Ensure that the peak charging voltage does not exceed 14.7 volts.

Otherwise, you can end up with a dried-out, non-conductive gel.