I have been reading up on blending at the info pop site recently and am currently running a 20% unleaded/80% WVO blend in Helga. So far the results have been very good with only one small problem on a very hot day that may or may not have been due to the petrol boiling and causing a vapour lock. There were signs this may have been the case and others that it was not so I have no idea what really caused the problem. That has been the only hiccup in 3 weeks running and it occoured in exceptional circumstances anyway.
From what I have read on the infopop site, blending WVO with Diesel CAN cause problems with waxes and " the dreaded White Stuff" dropping out and causing filter blockages and coating tanks and fuel pickups with slime and gunk. It appears to be a random but highly significant problem that many people experience and many have no problems with. It seems to depend on the Diesel people are using which can vary in it composition from refiner to refiner and be itself blended differently depending on the location it is sold in.
The general consensus is that you are SAFER using other substances to cut the WVO with like Kero or unleaded to avoid the problem in the first place. The problem seems to occour more in the colder weather so I would say you should be careful and do tests before using a diesel WVO blend. The problem appears to take some weeks to appear genreally so maybe you should mix up some test bottles and give them a chance sit. Of course the problem with that is that the diesel you buy to do the tests with would want to be the same as what you eventually use in your vehile. If the blend is changed as in winterised, your tests would be meaningless. You would really want to buy say a 200L drum, blend that fuel with the same oil you intended to use and then see if the two are OK and nothing drops out. I would suggest putting some samples in the fridge for good meausre.
As most maunfacturers list blending diesel with Petrol up to 30% to "winterise" the fuel, I would suggest that this may be a better alternative to blending with diesel. Petrol is a lot thinner than Diesel so you will be able to reduce the WVO's viscosity a lot more effectively with the same qty of Petrol than what you could with Diesel anyway.
As the weather is warming up, I am going to try cutting my blend back to 15% petrol and then 10% if that is OK and just vary the ratio according to the weather. 20% may be too much petrol for summer but perfect for winter.
As for coking, I think this is a subjective thing and depends on the engine and the blend you are using. Certainly in theoy a blend that is working properly won't have any ill effects.
As a saftey precaution, I am running a water injecton setup in the belief that this will prevent any coking problems and keep the cylinders and related parts carbon free. Some learned people here have questioned how effective this may be and as I haven't been doing it long or pulled an injector before I started, I don't know the engine condition to start with. If I do later look into the engine and find it clean and carbon free, I won't know if the blend was fine or the water prevented any problems. In any case, as long as everything is OK I happily won't care!
I would try some careful tests with the diesel blend but also give the unleaded a go and see how that works out for you.