Answer
(Fatwa: 318/122/L=1433)
(1) There are too many differences between Muqallidin and Ghair Muqallidin in usooli and furooi masail. Also there is difference of opinion in nikah and talaq rulings. Hence one should not marry them, particularly when the girl is a Muqallid Ahl Sunnah al-Jamah and the boy is Ghair Muqallid; because the girl will feel pressure and it will threat her beliefs and deeds.
(2) If the Ghair Muqallid imam does not abuse Ayimah Mujtahidin and takes care of Hanafis in the rulings of taharah and salah then you can offer salah behind him. However, if the imam of any other mosque have right beliefs and follows the sunnah then it would be better to offer salah behind him.
Allah (Subhana Wa Ta’ala) knows Best
Darul Ifta,
Darul Uloom Deoband