Can I mix Fluent API with Annotations Attributes in EF 6?

I have convention to put [Key] as an Annotation Attribute in Entity and rest of the configuration into FluentAPI (ForeignKeys mostly). I worked great, but then I found out that EF6 has this "magic conventions", that will create PK or FK if the name is in the specific format (I found out asking this question).

Then I thought, what if I'm doing something wrong and EF is saving my butt? And I don't even know that. So I removed all conventions, following this answer. Here's the code:

private void RemoveAllConventions(DbModelBuilder modelBuilder)
{
    var conventions = AppDomain.CurrentDomain.GetAssemblies()
        .SelectMany(a => a.GetTypes().Where(t => t.IsClass && t.GetInterface("IConvention") != null));

    var remove = typeof(ConventionsConfiguration).GetMethods().Where(m => m.Name == "Remove" && m.ContainsGenericParameters).First();
    foreach (var item in conventions)
    {
        try
        {
            remove.MakeGenericMethod(item).Invoke(modelBuilder.Conventions, null);
        }
        catch (Exception)
        {
        }
    }
}

protected override void OnModelCreating(DbModelBuilder modelBuilder)
{
    RemoveAllConventions(modelBuilder);
}

After that I got exceptions like:

CodeFirstNamespace.Item: : EntityType 'Item' has no key defined. Define the key for this EntityType.

The thing is.. Item does have [Key] attribute! When I add:

modelBuilder.Entity<Item>().HasKey(i => i.itemID);

The exception is gone.

Looks like, if you start Fluent API, you must put everything there. Is that true? Or I'm doing something wrong?