I don't usually write on this forum, but I feel it is justified in this situation.
First point: The reason this dera is not considered part of sikhi is because maharaj ji tells us not to do their sangat when we take amrit. We are told not to do the sangat of teer maleehe when we take amrit. This dera is from that linage.
Second point: Don't compare this dera to a brahmgiani like Sri Maan Sant Baba Isher Singh Ji Rara Sahib wale. If you listen to the story Baba Ji has a conversation with the muslim fakeer that possessed the person. After the instance the person was no longer possessed.
This dera on the other hand mess have a totally different tactic. People who have problems (i.e. no boy in there family, money problem, physical/mental problems etc) go to the dera as some random aunty usually recommends that they'll sort out their problems. Dhan Dhan Sri Guru Granth Sahib Ji maharaj already informs us that:
ਦਦੈ ਦੋਸੁ ਨ ਦੇਊ ਕਿਸੈ ਦੋਸੁ ਕਰੰਮਾ ਆਪਣਿਆ||
ਜੋ ਮੈ ਕੀਆ ਸੋ ਮੈ ਪਾਇਆ ਦੋਸੁ ਨ ਦੀਜੈ ਅਵਰ ਜਨਾ||੨੧||
(Ang 434)
Dadda: Do not blame anyone else; blame instead your own actions.
Whatever I did, for that I have suffered; I do not blame anyone else. ||21||
This dera, whatever the problem, state that someone has done some ridia sidia on them. Put them in doubts. Get them scared. Tell them they'll sort it. Only they don't. Most people within a few months are much worse than when they came. I've personally seem people who were perfectly fine before who due to a small issue go to these pakandees and after a few months they a very paranoid and irrational. After a sort time when the person gets worse they blame the ridi sidis and say to the victims that they need to go to there dera in the Himalayas and the pakandi baba will sort them out.
In Jap Ji sahib we are informed by maharaj ji that:
ਆਪਿ ਨਾਥੁ ਨਾਥੀ ਸਭ ਜਾ ਕੀ ਰਿਧਿ ਸਿਧਿ ਅਵਰਾ ਸਾਦ||
He Himself is the Supreme Master of all; wealth and miraculous spiritual powers, and all other external tastes and pleasures, are all like beads on a string.
They mess around in things which maharaj ji says are "Avra Saad" i.e. other tastes.
If we want to become good sikh we need to avoid this ridia sidia stuff and the pakandis that mess around with them:
ਛੋਡਿ ਛੋਡਿ ਰੇ ਪਾਖੰਡੀ ਮਨ ਕਪਟੁ ਨ ਕੀਜੈ||
ਹਰਿ ਕਾ ਨਾਮੁ ਨਿਤ ਨਿਤਹਿ ਲੀਜੈ||੧||ਰਹਾਉ||
Guru Maharaj Ji says avoid their sangat when we take amrit. Gurmukh pyare inform us to avoid them also.
So simply put avoid them.