In my humble opinion NiMh batteries are safe, if you have a problem is just because you did some very…. Very wrong.
I’m using NiCd/NiMh batteries since 1979 never had problems of fire even when I use an old kind of chargers.

I have a gold rule, always I charge under the battery C. If battery is 2000mA = 2A/h (C) then you could make a fast charge to 2A or more if the battery allows this.

Each battery has a charge rate chart, Obviously, when higher the charge current, higher the temperature at the end of the load will be, if you are using a good automatic charger.

I charge all the batteries inside the tanks, since 12 years now, but obviously there are some safeguards I take:
-Always use a FUSE immediately after the battery connector

-I use the table chart to select the better charge option, usually below 50% of C

-I try to setup the charger for the optimum delta peak of the battery this will make easier for the charger to understand when the battery is completely charge.

-I set a limit of time, for example: if I’m charging a 2000mA at 500mA, then I know that should be charged in 4 hours, plus a short time, we say 5 minutes. Usually this is enough if battery is completely discharger.

-If the battery is almost discharger then I use automatic discharge function to a low rate, we say 300mA ( for the one I mention above) UP to 0,8/1 volt per cell, which means 4,8/6 volts, 5,5 better.

From time to time I use to balance the batteries. Even the better brands which cell are matched come unbalanced after a time, mainly when the charge and discharge are fast. I use to completely discharge at 0,1 C and then charge it to 0,1C OR lower. Once the battery is charged, I set a low current to minimun the charger allows and follow during 15 minutes minimum. The ones already charged will easily dissipate the heat, the ones still didn’t arrive to the maximum charge will follow receiving charge up to match with the others.

Wireless charge is not a good idea, I fried few smartphones thanks this, the coil comes so hot that burns all around, is worst in the case of the phones and heat the lipo battery, but you don’t want to give extreme heat to your tanks.
A simple circuit showed in the image will keep you in the safe side, just have to make good solders and use good and new connectors.