All perfect praise be to Allaah, The Lord of the Worlds. I testify that there is none worthy of worship except Allaah, and that Muhammad, sallallaahu ‘alayhi wa sallam, is His Slave and Messenger.
The majority of Muslim scholars view that having witnesses to the marriage contract is one of the conditions of its validity. However, they held different opinions regarding stipulating that the witnesses should be 'Adl (i.e. trustworthy and righteous). Anyway, if this is something stipulated, it is not stipulated to investigate deeply its reality; however, it is sufficient that the witness's Fisq (dissoluteness) is not known.
Also, some scholars view that the one who does something prohibited as the result of misjudgment is not regarded as Faasiq (dissolute). Moreover, the matters that have become widespread in some countries such as Isbaal (letting garments reach below the ankle) and shaving the beard should not be regarded as a defect in someone's trustworthy and righteous.
Allaah Knows best.