I will admit to having a deeply-rooted bias against Lionheads, so take anything I say about them with that understood. I have seen very many Lionheads, and very, very few that came even close to what I hear is the breed standard. Most of them have had coats like Jersey Woolies in an unfortunate state of molt, and type has been all over the place. I have heard there isn't even a current breed standard, because the last person holding the Certificate of Development failed to get the breed accepted, and the current holder of the COD hasn't passed a showing yet, so it's "anything goes" on the show table, if a club will even let you show (they don't have to, at this time.)
Do you have any idea whether any of this breeder's rabbits have ever shown any sign of epilepsy? I understand that to be the most insidious of the problems with Lionheads, because of course you have to see (and recognise) a seizure to know that the problem exists. Normally, I have no problem with the idea of half-sibling crosses, but with this breed, and all the negative things I have heard about them, I wouldn't take the risk.