SilverJay

No they aren't, they're under their own section called mount traits. All of the other items like armour and staffs etc are under artifacts of power, and have the words artifacts of power on their respective tables. The only instructions for mount traits are that they are used by heroes on mounts, and you can have 1 per battalion. So unless there's an errata or faq, then I can't see a reason why named characters can't have them The mount traits are also a separate section of the battletome, and it might be similar to how named characters can get a spell from the lores

Do we know if named characters can have mount traits, because it's stated they can't take artifacts of power or command traits, but I can't find any restriction on mount traits

Vandus' command ability takes place in the combat phase, and affects HoS units wholly within 12" until the end of the phase