No, only those who who voted in primary can vote in run-off.
What about all the Dems who voted for Thad?He was openly asking them to do so.Do they get to vote again too?
Not true. If you are registered, you may vote in a runoff, but you may not crossover. This means that if you voted in the Democrat primary you may not vote in the Republican runoff. If you did not vote in either primary, you may vote in the runoff.