Our best friend is the officiant can he match the groomsmen?

I think that's fine!

Our friend is also marrying us, but he'll be wearing all black. Black suit, black shoes, black shirt, and we're getting him a nice bolo tie as his 'thank you' gift from us. But if you want your officiant to match the groomsmen, then I see nothing wrong with that!

You can dress your officiant however you'd like. If you do matching suits (which I think would look fine) I would consider a slight change to some other part of the wardrobe to distinguish him slightly from the groomsmen but still have everything look cohesive. Some options:

1) Different tie than groomsmen. Our officiant is a friend as well and both he and the groomsmen (and groom) are wearing floral ties, but the officiant's tie is a different pattern than the groom/groomsmen.

2) Same color tie but bow ties, with groomsmen in neck ties or vise versa.

3) Different boutonniere.

4) Different pocket square.

5) 3 piece suit vs 2 piece suits.

6) Suspenders or some other "accessory" that distinguishes the men.

I think having them in the same suits will help your photos look cohesive, but some other slight change will help distinguish him from being a groomsman without looking out of place.

I think it's fine to have your officiant match your groomsmen, but I would offer to pay for his attire since he is performing a role that is usually paid.