Googled suet and chickens cand came up with this.... it is aimed toward wild birds but has some good info.
http://www.natureskeepers.com/suet_vs_veg_fat.html
I don't know why they couldn't have suet. Molasses is a different story tho - it works as a laxative in chickens. Maybe another BYCer can give you more info on the suet?