Congregation’s prayer validity contingent on Imaam’s wudu

Imaam not having wudu invalidates entire congregations’s salaah.

It is not necessary to investigate whether the Imaam has done wudu or done properly. Dhunnu bi (a)l mu`mineena khairan.

However if one happens to know somehow that the Imaam does not have wudu. Or has done wudu by wiping over normal / cloth socks then one needs to repeat his salaah. This is because wiping over cloth socks is not considered a valid way of completing wudu according to all the classical madhhahib.