That vote is directly proportional to the amount of tokens they own. Technically (assuming all stakeholders vote) you need 51% of the currency supply to have total control of which delegates get elected.
That assumption is not safe. They should show in the block explorer how much % of the supply is actually being used to vote. I'd bet not much.
A couple of questions, since I haven't read documentation or code on DPOS:
1) How do you know the 101 are actually different people? most coins don't have 101 people who care.
2) Is the voting, electing, and the revoking of the right to be one of the 101 done automatically by the protocol? or is there human intervention (other than the voting)?
3) If I get 51% of the % of the supply that actually votes (which I bet is much less than 51% of the total supply) at any time in history (after the last update), then I could vote on the main chain, and then vote differently in an attacking chain. Then I could rewrite everything. Couldn't I?
4) If delegate N decides to ignore blocks N-1 and N-2 and build on block N-3, and then delegate N+1 builds up from block N, then blocks N-1 and N-2 would be skipped and considered missing? So 2 delegates could collude against the other 2? Now extend that 2 to 6 or to whatever number of confirmations are used...