Source: Fatāwā ʿUlamāʾ Ahl al-Ḥadīth, Kitāb al-Ṣalāh, Vol. 1, p. 244
Clarified for Practical Application
Even if the imam omits Rafʿ al-Yadayn or any other Sunnah act, it does not nullify the prayer.
While a Sunnah-adhering and righteous imam holds a higher virtue, the imāmate of one who omits Sunnah acts remains legally acceptable, and following him in prayer is permissible.
Reference:
Ahl Ḥadīth Suhādrah, Vol. 15, Issues 4–5
Clarified for Practical Application
❖ Question
Is it permissible to pray behind an imam who does not perform Rafʿ al-Yadayn (raising the hands) or neglects another Sunnah? Does such an action invalidate the prayer?❖ Answer
✔ Yes, praying behind such an imam is valid.Even if the imam omits Rafʿ al-Yadayn or any other Sunnah act, it does not nullify the prayer.

Reference:
Ahl Ḥadīth Suhādrah, Vol. 15, Issues 4–5