using beef suet to mix with ground deer meat

You don't want to use the hard fat as a mixing fat. There's a reason that stuff is only used in rendering bi-products.

Buy a brisket and mix that in if you want to use beef instead of pork.

I use ribeye trimmings as well. My local butcher gives it to me for free. I give him a call on Friday and give him a week and I’ll have 5-10 pounds I can pick up.

I made deer sausage with the fat from a Waygu cow last year. It was unreal......20 percent waygu fat 80 percent deer. You could probably do 10/90 as that fat went a long way.