In the All Breed Pedigree website somebody apparently has doubts on El Dere??? What's the story about that stallion?

Doubt is something in the eye of the individual beholder. As you can see from looking at his pedigree, there is none. All that is known is that his dam was supposed to be a Saqlawiayah Shaifiyah mare, but there no documented information at all. Nothing on who the dam actually was and not even strain for the sire. However, he was given to the RAS by King Faoud and used in the RAS/EAO breeding program so I suppose those who trust Faoud's word don't have doubts, those wo don't trust Faoud's blood might. That's really what it all boils down to for most of the old foundation horses. Human credibility.