I know there are at least 150 viburnum species and I've heard that some berries are mildly poisonous but, has anyone had a problem with berries and chickens.
Here is a bit of info for you. Hope this helps.The first link gives both good and bad plants for birds.
I have several shrubs, Viburnum, all berry well in Autumn, I have yellow berries, red, orange and I mainly grow them to feed the birds over winter along with many other type of berrying shrub / tree's,
All the birds love these plants, Robin, Thrush, Tit's, Blackbirds, Finches etc, so these are obviously NOT poisonous to these birds, but cant tell regarding chickens.
Birds are smarter than us and know what is edible and what is not, they know colours better than us and they know seasons better than us, so I would be surprised if these berries were harmful to chickens.
Good luck, WeeNel.