Sunni Student, It doesn't matter about Hizb Tahrir or not. What matters is communicating and understanding a fellow Muslim brother.
It is outright hizbiya- haram sectarianism, partisanship- to simply dismiss someone or render him a pariah because you think he is from a certain group.
And last I heard, HT are Muslim brothers, period. So what is this about if Caliph likes HT, or listens to them, etc.? ....