I tried, and sadly not. HexKit uses individual tiles instead of a large image file.
So, for example, their Spaceland tile set is set up like this:
Folder: Spaceland
Therein included are other Folders like "Nebulae", "Anomalies", "Planets", "Asteroids"
And then in those folders you have individual hex tiles as .PNGs
I don't know if this would be feasible for you to split your hex set up into those sub-folders and individual images. But it WOULD be greatly appreciated! :)
Unfortunately it looks like HexKit hex's are vertical instead of horizontal, so my kit doesn't really line up with the program well. If you're interested in trying it out for yourself, you can grab all the hexes (and more) as individual PNGs from this incredibly lovely github that Yairm210 setup:
https://github.com/yairm210/UnCiv/tree/master/android/Images/TileSets/FantasyHex...