Ref. No. 1439/42-867
In the name of Allah the most Gracious the most Merciful
The answer to your question is as follows:
There is a difference of opinion about the prophethood and life of Hazrat Khidr (as), so it is difficult to make a definite decision. However, according to the preferred view, Hazrat Khidr (as) was a prophet. It is allowed to make dua to Allah with the wasila of an angel, a prophet and a wali. We couldn’t find any narration about asking the angels to pray.
And Allah knows best
Darul Uloom Waqf Deoband