Can I use my Westjet lounge voucher at this lounge. I am flying on a Westjet/Delta flight

No way Jose

Not unless you are flying premium or first class. We just wear through Atlanta and had westjet premium and delta first class. They let us in. But said they could not use westjet vouchers

Just finesse yourself in!!!

I'm just guessing but I'd say no.

Good one, unfortunately I have not come across this scenario. Can't say