Don't think that the BA/nillarines dex would work as all the points values of the vehicles are different, for example rhinos are 15 points extra. Also you would have to have unit entries that say you can only use these with X army, thunderwolf cavalry is an example of this, can you imagine how many kids would turn up to play with ultramairnes on wolves?
Its not the best system, having multiple dex's but it seems to work alright.
When evil seeks to overcome good
And firepower ovecomes the spoken word
Then death shall rain from the sky on wings of blood
And retribution will be swift