You don't put them in the Razorback, but you can get them one just to get an extra tank in that HS slot.
The problem I see with Henchmen-Razorback spam is they clash. Henchmen want to get close to get the most out of the cheap spam of plasma/melta/flamer/CC. Razorbacks want to stay at long/mid range.
Techmarines are a cheapish way of getting Orbital Strike Relays. One with a Conversion Beamer, 3 servo-skulls and an OSR comes at almost 160 points, and seems like packing a good punch. Since GKs seem to have little access to pie plates, they may not be a bad idea. Heavy Psycannons are rare, and psyker squads really unreliable. I just wonder if the OSRs will be any good. :/