A vow of poverty is one thing, having to beg for your food is another.
And even if this is 100% true, I don't see that as such a big deal. People are imperfect.
When donations are solicited for helping the poor, and are not used for that purpose, that's what we call fraud. That's just as true whether the funds are used for gambling sprees or just sit around in a bank. Mother Theresa took money under false pretenses, pure and simple.