Does the order for clustered index have the same constraints as non-clustered index on search?
Just think left-to-right, until you hit a gap. 

For Q1, SQL server can search for ad_account_id (assuming that was in the index and you had a typo in the index definition), and then scan those with that value. 

For Q2, SQL server can search for ad_account_id and group_id and then scan those.

For Q3, SQL server can seek for all columns in the WHERE clause.

So, yes, the same principals applies to a clustered index as for a non-clustered index.