EF6 definitely supports geography types in stored procedures (as did EF5). Although I've only worked database first, I pulled this (modified slightly and simplified) from the EDMX file. Hope it helps.
public virtual ObjectResult<MyClass> MyStoredProcedure(System.Data.Spatial.DbGeography location, MergeOption mergeOption)
{
var locationParameter = location != null ?
new ObjectParameter("location", location) :
new ObjectParameter("location", typeof(System.Data.Spatial.DbGeography));
// EDIT: Neglected to copy this part in during original post
return ((IObjectContextAdapter)this).ObjectContext.ExecuteFunction<MyClass>("MyStoredProcedure", mergeOption, locationParameter);
}