Not directly related to the NiMH cells under discussion but:
Recent incidents with Lithium batteries, fire at Durham police HQ and on Boeing 787 aircraft, reinforce the case for not taking risks with batteries, particularly cheap unbranded ones. In both cases it is reported that the batteries were on charge at the time. The Boeing battery was said to be a Lithium ion, not sure about the Durham one.
Having had first hand experience of incidents with Lithium cells, both primary and rechargeable types, I wouldn't say don't use them but do take care. Don't leave Lithium ion on charge unattended and watch for warning signs like overheating. The amount of energy released from even small cells when things go wrong has to be seen to be believed.
Regards