A tube that can be used in a power amp output stage can easily be used in a preamp as a voltage amplifier, it will be loafing. There are a few problems though. Power tubes tend to be more expensive than traditional preamp tubes, and using DHT tubes in a preamp means that you have to deal with the noise that the filaments of these tubes tend to introduce in traditional configurations. A little noise introduced in the output stage might not be a problem but likely will be in a preamp.
I suggest contacting
Experience Music as he can build you whatever you want and is well experienced in dealing with the noise issues.