The answer is Yes.
The following example shows the criteria for 3 fields (i.e. 3 combo boxes):-
SELECT [Field1], [Field2], [Field3], [Other Fields]
FROM [TableName]
WHERE ([Field1]=[Forms]![FormName]![combo1] Or [Forms]![FormName]![combo1] is null)
And ([Field2]=[Forms]![FormName]![combo2]...