I did end up figuring this out by the following:

select b.Name, a.Category, COUNT(a.OrderNumber) as 'Total Orders',

((sum(

CASE

WHEN b.UserID = a.EnteredUserID and c.OrdSourceID <> 'PROTOCOL'

THEN 1

ELSE 0

END) * 100 / nullif(COUNT(a.OrderNumber),0))) as 'Phys Entered %',

((SUM(

CASE

WHEN b.UserID <> a.EnteredUserID and c.OrdSourceID <> 'PROTOCOL'

THEN 1

ELSE 0

END) * 100 / nullif(COUNT(a.OrderNumber),0))) as 'Other Entered %',

((SUM(

CASE

WHEN c.OrdSourceID = 'PROTOCOL'

THEN 1

ELSE 0

END) * 100 / nullif(COUNT(a.OrderNumber),0))) as 'Revised Order %'

from OeOrders a

INNER JOIN OeOrders2 c ON a.OrderID = c.OrderID

LEFT OUTER JOIN DMisUsers b ON a.ProviderID = b.ProviderID

where (a.OrderDateTime between '2012-01-01 00:00:00:000' AND '2012-09-09 23:59:59:999')

and a.Status <> 'CANC'

and b.Name is not null

group by b.Name, a.Category

order by b.Name, a.Category