That would be even better. If it's not accepted, report it.
PIV says that demandi is transitive and gives examples such as demandi iun pri io and li demandis ŝin, kion ŝio faras tute sola and kial vi min demandas pri bono? and ne demandu scienculon, demandu spertulon that indicate that the direct object is the person asked.
Z used "demandi al" in La Nova Testamento, S. Luko 9:45 "ili timis demandi al li pri tiu diro"
I'm not doubting you, but that seems really strange to me. I would have thought the implied "something" would be the direct object and "him" is the indirect object.
You do have that with peti which can also be "ask" in English, but in the "request" sense rather than the "post a question" sense -- that can be either peti iun pri io (ask someone (obj.) for something) or peti ion de iu (request something (obj.) from someone)..
Though neither uses "al" which is usually associated with "indirect object".
His diction leaves something to be desired. I couldn't tell the difference between demandis and demandos.
Type what you hear! If so i should write "mi demandos kaj li" which would make no sense
Zamenhof used "Demandi al iu pri io" several times. "Demandi ion al iu" can also be found but seems infrequent.
For me I see it like the verb "shout." You wouldn't say, "I shout him," but "I shout at him." It doesn't answer the question from the Esperanto-side of the equation, but it does provide a way to look at the verb that makes a little more sense.