Is "parading the groom with religious poems" using the tambourine and mizmar, or just poems, considered a Bid'ah (innovation), and does Bid'ah include matters of custom?

The reprehensible Bid‘ah (innovation) in Islamic law is specific to acts of worship, and the default rule concerning them is prohibition unless there is evidence of their permissibility. It does not apply to customs and traditions. Therefore, the mere fact that an ordinary matter was not done during the time of the Prophet, peace be upon him, does not indicate its prohibition, as long as it is not among the devotional acts. The religion of Islam permits playing the Daff (tambourine), permissible singing, and spreading joy and happiness at weddings, while forbidding the use of wind instruments and other prohibited musical instruments.