Yes it is. I bought the Giant mik rack from the Giant website and ordered the trunk bag from Amazon. It's a Basil mik trunk bag with a click on lock and key. Great bag.
Is is possible that you could take a photo of how the bag fits onto the rack? Particularly how much space there might be on the sides? I'm asking because I've never seen how a MIK bag fits onto the rack and I use Ortleib panniers that hook onto the side rail of the rack. I'm afraid that with the panniers mounted I wouldn't be able to attach a MIK bag on top. And I'd have to order the bag without knowing if it would fit.
When I get home I'll take a photo of how my Ortleib panniers fit onto the rack and maybe you'd be able to see if the trunk bag would still fit.
Here are a couple of photos which show the "hooks" that my Ortleib panniers use to hook onto the top of my rack. I'd like to buy a MIK trunk bag but I have no way of knowing if it would still fit when the panniers are attached. And nobody in my area has MIK stuff that I can check so I'm reluctant to order sight unseen. Can you please take a look and tell me what you think?
I think this Basil bag would fit on top of your panniers. The Mik plate fits inside the bottom of the bag with a bit of bag overhang. I took a photo of the Giant rack (which looks a bit different than yours - mine doesn't have the blue bungie) , the bottom of the Basil bag with MIK plate and the sides. Hope this helps. Btw. I had a hard time trying to find a trunk back with MIk plate attached and finally bought this bag on Amazon.