Lightning,
We should be carefull with our speech. There are so many incredible stories of harmony between Gelug, Nyingma and other schools out there such as this one from Tomo Geshe Rimpoche's bio on this website:
'Tromo was changed completely by Domo Geshe Rinpoche’s presence. The Bönpos at Pemukang sent yearly New Year offerings to him at Dungkar Gonpa, as did the Nyingmapas from nearby Kyiruntsel, where a room was kept ready in the monastery for Domo Geshe Rinpoche. Eventually, Rinpoche instituted several practices that brought the people of Tromo together in greater harmony. One of these was a yearly joint reading of twelve collected works (sung bum) at Kampu Dzong in Upper Tromo by the different religious traditions. Another practice was a special Guru Rinpoche (Padma Sambhava) ritual. Dungkar Gonpa had acquired an especially holy Guru Rinpoche statue, said to have been blessed by Padma Sambhava himself. When the owner was on his way to India with the statue, it spoke when passing Dungkar Gonpa. “Take me to where that sound is coming from,” it said, as the long trumpets sounded from the monastery on the hill. The man did, and Geshe Rinpoche gave him what he needed. Not much later, it is said, Domo Geshe Rinpoche found a Guru “fulfillment of wishes” (thug drup) text near Dawa Trag, a rock not far from Dungkar Gonpa bearing a spontaneous manifestation (rang jön) of a moon. Shortly thereafter, someone came with many copies of the same text for sale. Geshe Rinpoche bought all of them and, once a year, the Dungkar Gonpa monks performed the ritual.'
Tomo Geshe Rimpoche is a very special and unique Gelug lama and neither the Bonpos nor the nyingmas of Tromo Valley had any problems with Dorje Shugden. Dorje Shugden helped in creating harmony in Tromo valley. It is true that we should not mix in the end. But in the beginning, one can and should investigate all four schools. I think this is what Contentment (got it right this time!) is trying to do and Dorje Shugden can help him find his path even even if it is in Nyingma.
Also, it is true that Dorje Shugden can sometimes punish high gelug lamas who abandon the teachings or mix their practice with other stuff. But this is because they are acting contrary to their previous commitments and mind generation and are in a position of influence over the teachings and beings. We ants should have no fear because we are not included in this category.
Also, since Dorje Shugden is a Buddha, he helps and protects all sentient beings. This has been said and written many times. That is, he will help and guide anyone requesting Him irrespective of race, religion, color of hair, sexual orientation, etc. Even if Christians, Muslims, Jews or believers of doomsday cult rely on Him, they will definitely receive benefits in this life and others. Remember, He is the futur last Buddha of this Aeon.
Finally, the remaining 400 years of Gelug culminate with the Shambala war. This 400 years can be extended by prayers and dedication. In the same manner as tsongkhapa's lifespan was increased thru special prayers.