In his book Bhai Rama Singh Ji mentions that because he was
constant in doing Amrit Vela with Sadh Sangat he met a Shaheed Singh and had darshan
of Khalsa Raj in his dream.
Bhai Desa Singh Ji was another Gurmukh who use to do lots
of seva to sangat and one day on a yatra do ( patna sahib?) he
received Darshan of Guru Sahib and Guru Sahib told him the
Rehat Maryada of GUrmukhs which included some of the following verses:
ਆਗੇ ਆਵਤ ਸਿੰਘ ਜੁ ਪਾਵੈ, ਵਾਹਿਗੁਰੂ ਕੀ ਫਤੇ ਬੁਲਾਵੈ
When you see a Singh in person greet him with fateh( lol, inside joke for NS Veer Jeeo)
Bhai DEsa Singh Ji Rehatnama
ਰਹਿਤ ਪਿਆਰੀ ਮੁਝ ਕਉ ਸਿਖ ਪਿਆਰਾ ਨਾਹਿ ।
Those that follow Rehat are my beloved Sikhs ( pyaarey)
Bhai Desa Singh Ji-
ਦੁਹੂੰ ਗ੍ਰੰਥ ਮੈ ਬਾਣੀ ਜੋਈ। ਚੁਨ ਚੁਨ ਕੰਠ ਕਰਹਿ ਨਿਤ ਸੋਈ'। (ਰਹਿਤਨਾਮਾ, ਭਾਈ ਦੇਸਾ ਸਿੰਘ)
So it seems that those people who follow rehat and serve sangat
are the ideal candidates of having mystical dreams.
ਸਤਿਗੁਰਬਚਨਕਮਾਵਣੇਸਚਾਏਹੁਵੀਚਾਰੁ॥