Yes, assuming they're not faulty you can charge them quite safely in the Canon charger, but charging stops once the light is constant and there's no need to leave them in the charger after that.
The standard Li-ion batteries can stand around 300 charge cycles, after which they're toxic waste.
I have one that's over six years old (came with a Canon G2) and it still works, but doesn't hold as much charge as newer ones.