Hi
I've come across a keyboard on the aftermarket, labeled as a Cherry G81-3000.
Now, from what I can see, it's a G80-3000, not a G81. Can anyone help me verify?
If it's a G81, do you know whether or not the keycaps are Cherry MX compatible? Also, dye-sub, Double shot legends ?
Thanks very much 
The easiest way to find out would be to ask the seller for a picture of the rear label. The line of interest is the "Article No." line, which will tell you whether it's a G80 or a G81.

It's sometimes possible to know whether it's a G80 or a G81 without seeing the label if the photo is top-down, especially if it's a flash photo, since you can usually see the G81 membrane or the flash reflection. From the angle of the picture you posted though? There's no way to tell.
Regardless, the caps will be fully MX compatible. Winkeyless G81s use the exact same set of caps as winkeyless G80s, or any other winkeyless MX keyboard. Also, the caps are doubleshot on this particular model. You can usually tell if the keycaps are doubleshot or dyesub by eye; the difference in legend contrast is fairly noticeable.
Very nice board by the way, good luck getting it. I wish I could get one like that.