I have friend who has several dump trunks full of asphalt
millings. I would like to excavate the gravel and dirt and put down 4
to 6 inches of the millings.

By "millings" you mean old waste asphaltic concrete from scarifiers?
"Asphalt" is petroleum tar, not asphaltic concrete (asphalt plus
gravel).

That recycled stuff is basically a low-quality gravel, weak and brittle,
that can only be used in small proportions in new paving material for
the sake of getting rid of it. And that has to be done by lots of heat
and mixing with fresh asphalt in a big mixing plant. Not something you
can accomplish in your driveway.

There's a reason this old material was torn up. It's no good for paving
any more. You might as well try to pave with kitty litter or bread
crumbs.

My question: Is there any product available that would help in
bonding the material when I put it down?

Yeah, it's called asphalt. See above.

Or are the retailer sealers adequate?

You mean the water emulsions of asphalt? Forget it.