Dukhat wasn't part of the Grey Council.
He occupied the Leadership position that Delenn was nominated for and turned Down.
IOW, he outranked the Grey Council and have Veto authority over their actions.
His decision Not to use that authority when the Minbari first learned about Humans was what, about ten years later, led to the Earth Minbari war when Humans learned about the Minbari.
Dukhat chose Delenn when she was an Acolyte and groomed her for grey council membership and as his eventual replacement.
Openly enough that she was Know to be the "Chosen of Dukhat", his heir apparent.
There are indications that he knew all along about her having Valen's DNA.
His contact with the Vorlons could give rise to all sorts of speculation about whether they might have Suggested Delenn to him.
Or, he could just be one of those people with an uncanny eye for Talent.
The 10 points of light question has it's answer in Dukhat's position. That 10th spot is His.
Remember that, after Neroon sacrifices himself, she indicates that 10th spot and declares it will remain Vacant until the Mourning Period for Neroon is over, just as was done for Dukhat. 10 Cycles of mourning in Dukhat's case.
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Do not ascribe your own motivations to others:
At best, it will break your heart.
At worst, it will get you dead."
