The rabbit at the end who takes Hazel into his Owsla is not El-ahrairah, but is the Black Rabbit of Inle instead.The Other Wiki's synopsis states that the rabbit who appears before Hazel at the end is El-ahrairah, but I'd like to suggest that it is the Black Rabbit instead. First, if you watch the film, you see what we know is the Black Rabbit when he guides Fiver to find Hazel after he gets shot. At the end of the film, we see a black ghost of a rabbit, but this one has more defined features. However, if you watch closely, not only does this rabbit's eyes glow red (just like the Black Rabbit's did), but also while it is bounding away from the warren, it looks just like the rabbit that led Fiver down the hill earlier in the film. Second, if you think about it, the rabbit being El-ahrairah doesn't make sense — El-ahrairah is a folk hero. Most rabbits believe he exists, but in both the book and the film, we're never shown beyond a doubt that he does indeed exist, truly. However, in the book, Fiver has a dream where he directly meets the Black Rabbit, and the film has that awesome "Bright Eyes" scene where he chases said Black Rabbit. Third, If that really was El-ahrairah, then that means El-ahrairah is actually dead (shouldn't he be in the Black Rabbit's Owsla now, then? The book teaches us that the Black Rabbit is even more clever/powerful/etc than he is). Fourth, the book teaches us that the Black Rabbit does indeed have an Owsla; as seen in El-ahrairah and the Black Rabbit of Inle story told two-thirds of the way through the book. Where else would the Black Rabbit have gotten his Owsla, except from truly exceptional rabbits that lived and passed on? Hazel definitely fits that category.
Bigwig was invited to join El-ahrairah's Owsla too.Sure, Hazel got them out of Sandleford and to Watership, but after everything Bigwig did, you can't say that he didn't deserve a spot in the Owsla.
The story of Cowslip's warren is a religious allegory.The part about Cowslip's warren is an allegory for the readers, showing that civilization, art, and lesiure are parts of a trap set by Satan to ensnare the souls of humanity, and hard work and fellowship in a natural life are part of the path to salvation.