The company that I work for has 3 coaches, however these are only for Schools work, they do not run at any other time, I am not 100% sure what licence they need to run on (whether an O licence is needed, I assume there would but not sure as to whether or not it would be less strict than if it was service), we have had calls before for coach work and have sent them to the local coach company up the road.
On the taxi side of it, I have never worked for a taxi company that hasn't "shared" the assets of others I worked in the office for a private hire company in Edinburgh and because we didn't have WAV (wheelchair accessible vehicles) because at that time the council did not allow you to have them as private hires, we had to take the hire and then ring up a black cab company to do the job and do a deal on the metered cost because private hire companies did discounts that the taxi companies couldn't. It worked because we were cheaper on out of town work and would get phone calls from the taxi companies for OOT or if they were really busy for some help.
All of the companies where I am now in the South West do it, although some companies tend to disassociate themselves when questioned, you don't want to be seen being cosy with your fiercest rival do you? even though you do 9 times out of 10 help eachother out. This may have been the case when some members here have been ringing to gain information, whether or not it was for their own means or to try and possibly out a wrong un (which I am not accusing anyone of) then you would certainly get people's backs up.