yes
the Orthodox do not have "orders" like the Catholics and thus do not need to differentiate with fancy stuff or color codes
also keep in mind that male orthodox priests and monks do not shave their beards
don't know about the nuns though 
correct former user. There is some "orders" in the greek orthodoxchurch, but the differences are minor (and no visual in 28mm), so no problem with them. the monks have different caps.
available models:
Old glory: pack COS-13, cossack clergy (from their cossack wars range
http://www.oldgloryminiatures.com/products.asp?cat=116&pg=2The clergy clothing has not been changed over the centuries so they are OK.
The last two make an ideal monk and priest. The first row is much more in active poses.
Some of them are also suitable for Greek, Bulgarian, Serbs, Armenian etc clergy. No need to make any conversion. They can also be used in other eras, even moden ones.Just a minor info. Orthodox priests operating in Western Europe do not wear special garments outdoors and usually have small beards. they look more like a protestant or anglican pastor.
A more elaborate clergyman, half civilian clothing etc can be obtained by brigade games form the command pack BG-SIER001
http://www.brigadegames.com/Merchant2/merchant.mvc?in their strom in the east range.
a good nun can be found from WW1 german nurse again by Old glory pack WW1-113
http://www.oldgloryminiatures.com/products.asp?cat=311&pg=2just paint her black