Примерно так, может быть, использовать индексы (если они у вас есть):
select MembersInCountyCat = count(*)
from (
SELECT MemberID
FROM Member
WHERE NYKACountyID = @NYKACountyID
AND NYKACatID = @NYKACatID
AND ProfileTypeID <> 1
union
SELECT MemberID
FROM Member
WHERE NYKACountyID = @NYKACountyID
AND NYKACatIDExtra1 = @NYKACatID
AND ProfileTypeID <> 1
union
...
union
SELECT MemberID
FROM Member
WHERE NYKACountyID = @NYKACountyID
AND NYKACatIDExtra10 = @NYKACatID
AND ProfileTypeID <> 1
) t
union
сделает эти MemberIds уникальными