mixing lead acid nimh
Take care that the original way to recharge the lead acid batteries is not working properly with the NI-MH batteries too.
You risk to make an explosion due to surcharge of the batteries connected.
The recharging of the NI-MH batteries is something quite complicated, involving current, temperature, voltage and time.
If You are not recharging the batteries in your circuit I don't see any problem.
About vibrations, tested on one applicatoin until 8G random without any problem.
Mandi