It's pretty sketchy, tbh.
I give it a non-zero chance of being rejected outright.
Unfortunately the Eagle CAM rules supplied by most cheap board houses don't work in Altium, so I did it by hand. I used different Gerber layers for the internal slots and the outside perimeters, and I have no idea if that will work. Worth a shot! I guess!
I delayed a little long with this, so it's Chinese New Year, and they won't even be back at work until the 27th. And won't start catching up with the backlog until even later. I guess I'll see it in four to six weeks!