Can I use Ni MH for outdoor umbrella lights instead of Ni-Cad as the manufacturer suggests

I recently purchased umbrella led lights for my patio umbrella which use batteries which is so much nicer than having to run extension cords from the old kind. The manufacturer suggests using rechargeable ni-cad batteries and I bought Ni MH. Will there be any damage if I use the Ni MH?

With the slightly higher voltage light output will be a little brighter and bulb life will be slightly shortened.

I think the main reason for the recommendation of using NiCd in these devices is that the charging circuits for NiCd batteries are simpler and these lights are very cheaply made.. NiMH batteries are more easily damaged by extended trickle charging as you would see in a solar powered light and the extra capacity that is the main selling point of the NiMH battery probably really isn't needed anyhow. My lights run all night on NiCd batteries, plus the deep cycling is actually good for NiCd batteries.

That manufacturer has probably been making and selling the lights long before reasonably priced NiMH cells became available. He just hasn't updated his information.
Go for it.
You could also use a gel cell rechargeable of similar voltage, if the battery is close enough to either 6 or 12V.
For any rechargeable, of course, you need a suitable charger.