I 3D printed some Astartes riding cybernetic lions to make my own thunderwolf cavalry for my Blood Ravens, just to have some cool models escorting my Landraider
That Deathwatch list has so few units! I fear it could easily get swarmed by fast moving units. Also, no Infiltrators and no Scouts is kind of missing a lot of what Vanguard brings to the table for DW IMO. Any reason why you don't include a bike in the Proteus? Could make use of it's speed to help reach the intended target.