Well, I have samples coming from Celestion and cabinets already with Eminence drivers in them as well, and we should be able to do an a/b comparison and decide which direction we want to go. I agree though, that Celestion tends to be closely associated more with guitar speakers, although they do some very good bass stuff. One of my old bands had Celestion 15" 1000 watt drivers in the bass bins that were absolutely thunderous !
I'm quite sure that when you've managed to carve a name for yourself in the speaker-for-instrument-amplification business, you have gotten a thorough understanding of how a speaker works along the way.
I am fairly confident that Celestion can make decent bass speakers.
The way I understand it, cabinet companies can order drivers built to their spec (within given limits, I suspect).
Furthermore, I doubt that as a cabinet maker, you will be judged by the label that is stamped on the rear of the speaker. Bass cabinets usually are not open back, so nobody gets to see the backs of the drivers anyway.
You'll much rather be judged by how much volume you can squeeze out how small and light a package,
and of course by how that thing sounds.
With guitar amplification, the cabinet often is an open box which main job is it to give the amp a place to sit on and make sure the speakers are upright. It is quite common to buy an unloaded cabinet and put in the drivers you like, or change the drivers in a cabinet for ones you like better.
In bass amplification, the cabinet is much more important and it is seen as a system in which the driver plays only a part. It is a rare thing that people get the idea of rolling drivers and when they ask others about it, they mostly are discouraged from doing so.
What I'm trying to say is: The guitarist looks at the speakers while the bassist looks at the cabinet.