Interesting and confusing, or even contradictory is that India, while not bold enough to defy China's sovereign claim on Tibet (fair to say not a country is bold enough), indulges itself in playing trick of harboring Tibetan exile government, which seems to be supported by CIA.
'Was' would be the right choice, after 1962 Tibetans refugees were trained in case of a future war with China, however after normalizing ties the Tibetans form a border police force .
Was it China hasn't provided sufficient evidence or their existence and activities or India simply ignores what it sees and hears?
Forget sufficient evidence , your Govt hasn't provided any evidence or even made a claim of their supposedly anti-Chinese activities
On the whole Tibet is incomparable in the current context ,
Tibetans don't go on a killing rampage in any Chinese city.
Tibetans aren't the one creating trouble in Xinjaing.
However the groups China has attempted to stall are affiliated to Al-Qaeda , which has vowed revenge for Xinjiang also caused problems in the CARs.