All praise is due to Allah, and may peace and blessings be upon the Messenger of Allah.
First: Are miracles granted to the righteous real?
Yes. Miracles granted to the righteous servants of Allah are real. They may occur to some of His righteous servants who adhere firmly to the Qur’an and Sunnah. One example is a jinn leaving the body of an afflicted person through the blessing of a righteous person's supplication and obedience to Allah.
A story has been reported about Imam Ahmad ibn Hanbal (may Allah have mercy on him). He sent his sandal to a young woman who was suffering from seizures and instructed the jinn to leave her. The jinn then left her, as mentioned by Ibn Abi Ya'la in Tabaqat al-Hanabilah.
Such miracles do not require dervish rituals or religious innovations. Rather, they are blessings bestowed by Allah upon His righteous servants.
Second: Are this person's practices considered a miracle?
The dervish rituals you mentioned, along with piercing the body with skewers without feeling pain, do not constitute evidence of a miracle. These practices are not consistent with adherence to the Sunnah, whereas miracles are granted to those who are obedient and steadfast in following it.
Nevertheless, this does not rule out the possibility that the person treats magic through legitimate Islamic ruqyah, as other ruqyah practitioners do.
Third: Is it permissible to seek treatment from this person?
If trustworthy people confirm that he does not use magic or commit acts of shirk, such as seeking help from the dead, and that he treats people only through the Qur’an and legitimate Islamic ruqyah, then there is no harm in seeking his help.
However, it is preferable to seek treatment from a ruqyah practitioner known for righteousness and adherence to the Sunnah.
Conclusion: Miracles granted to the righteous are real, but they do not involve dervish rituals or religious innovations. Rather, Allah grants them to His righteous servants who remain steadfast in obedience to Him. It is permissible to seek treatment from someone who adheres to legitimate Islamic ruqyah and avoids magic and shirk, although a practitioner known for following the Sunnah is preferable.
And Allah knows best.