I am currently using an IPad Mini 4 with the Mavic. I am mounting the Mini 4 directly onto the controler. Does anyone know if the Hoomdam HAV1 will work for this configuration?

Not, directly, no. You'd need to also buy a mount like this one.

Leak

Sort of. There will be light leaking. I use an iPad mount and there is no leak.

You could always buy a couple feet of 1" velcro and just use the hook side to block the leak. Probably around $1.