If buddha never got angry, why do so many buddhist teachers say anger is inescapable? Some buddhist teachers say anger is inescapable, or even necessary and healthy, are they not enlightened ?
Because teachers, or even if they are arahats, are not Buddha.  They often err or have some imperfection in their teachings.  They may have destroyed all or some of the fetters but they are not perfect as Buddha in Dhamma (both in seeing and how to articulate it).  In Ani Sutta, Buddha said not to lend ear to new teachings. I have not seen "anger is inescapable, or even necessary and healthy" in any sutta that could be credited to Buddha's original teachings.  As for myself, I disregard it. 

PS.  I certainly not to be disrespectful to your teachers.  They may be imperfect in their teachings but it is still a good idea to hangout with people who are virtuous in their precepts.  IMO. 

PS2.  wanting to be near, approach those with virtuous actions, keeping precepts is a sign of Saddha.