It is but rituals are horrifically dangerous to any and all people. I do not think the elves would teach them to any who are not magic specialists, and to their minds those are the archmages.
As the top elf magic specialist Teclis would know them and as one of three mages facing massive Chaos invasion he'd be incentivised to teach them even to humans as long as he's convince they're going to help rather than hinder.
Elves might actually be more inclined to teach dangerous stuff to humans (as long as it doesn't massively upset the balance of power) since they care a lot less about human mages blowing themselves up fighting Chaos as long as the process is efficient.