All of the v3 sabers are MHS compatible. This means that if you were to get the Initiate v3 and specify that you wanted the Catalyst pommel that is what you would get and it will fit. All of the MHS sabers can have any MHS pommel. The catalyst is MHS compatible, which means the pommel will fit and v3 saber. Hopes this helps.
This is true.
I think he might also be wondering if the Catalyst pommel will sit flush with the body of the saber.
When I took a picture for a member of the Archon V2 body with the Catalyst pommel, it wasn't flush with the body.
I can try tomorrow with the Catalyst pommel on my Aeon V3.