I'm more impressed by Teachers who show loving kindness - it's a clearer sign of realization for me. Anyone can show the example of getting angry, it's nothing special. It's possible that these Teachers are clearing the obstacles of their students, but quite possibly they are simply deluded? It's good to have pure view of such actions but I feel the time of display of 'wrath' is over as it simply looks like someone who cannot control their mind.
Everyone's view is different according to their experiences. I think how we can tell if the Gurus are showing vajra anger or are deluded is:
1. whether there is agenda - does the Guru gain anything - what is his or her motivation?
2. whether the emotion stays - i have read of Gurus who can scream at one person then when another student comes by, he laughs and jokes with them - an immediate switch of temperament which shows that the anger is completely under control and manifested.
I believe that Tantra is the path of where we learn to transform our negative emotions and attachments into positive ones. If we are fortunate enough to have a tantric master, the master will create situations where our negative emotions will arise in order for us to conquer them. If the master waits until the situation arises on its own, it wastes time and the master may not be around at the time of that emotion arising.
Tantra is fast track - i remember reading that it is likened to a snake in a bamboo pole, with a fire burning at one end. There is only one way out, there is no side exit, there is no reversal. While it is the fastest path, it comes with risk and at a possible price.
When the Guru is wrathful to teach the students, the students may not be able to take it and leave the practice. This is a risk the Guru always takes. The wrathful method is not a pleasant one for the student, especially when it aims to point out and destroy, like the precise laser scalpel of a neurosurgeon, the very attachments which we have spent lifetimes lovingly cultivating.
There is also risk that the students attempt to be wrathful like their Guru, but without attainments, the students are usually showing destructive anger rather than constructive vajra anger. For example, you can often see how some Buddhists are very angry at other Buddhists who do not agree with them and it becomes very nasty. Who are we to judge? Let our Lamas advise us. We are nowhere near the levels of the Lamas.
If someone else believes something (eg. the tulku system) because their Lama propagates it, who are we to judge if what their Lama is teaching the right thing or not? As always the best way to check is the motivation of the critics - is it from ego of wanting to be right? Or even senior students within the same Buddhist organisation - they may feel more arrogant because they work closely with the Guru, and they will use their situation to bully the other students. The ego is so sneaky and will manifest in many creative ways.
Anyway, i do believe that a 'wrathful' teacher is extremely compassionate - to risk everything for the transformation of his or her students. The students must have total faith in their Guru in order to use the situation to transform for the better than as a situation which creates the desire for flight - another (stupid) manifestation of the ego.
I've read the biographies of Chogyam Trungpa Rinpoche who often used wrathful methods on his students. Personally it's a bit scary for me but going back to the surgery analogy, any serious surgery is scary but necessary to improve our life - without it, we'd die sooner. It'll be painful and the recovery process arduous, depending on how extensive the surgery, but afterwards, the reward is worth it.