Oh, lots of actors playing Vulcans show emotion. Look at Spock yelling in the first few TOS episodes. Really, John Rubinstein as Minister Kuvak was hardly any more placid in his delivery than V'Las.
Anyway, people in power often have private indiscretions that are tolerated because of their power. A Vulcan administrator having outbursts of emotion might be akin to, say, a US president having an affair. The people in the administration who know about it may disapprove privately, but they tolerate it and mainly just try to keep it out of the papers. Everyone has flaws, so it'd be pretty ridiculous to toss out an officeholder the first time they exhibit an imperfection.
So the High Command wasn't going to throw out V'Las simply for raising his voice. Bombing civilians, framing them for terrorism, and attempting to start a war on a fabricated pretext are a touch more serious than that.