Are they at all slippery when wet / do they have good traction? We'll be walking on them in wet ski boots, and I'm concerned that ski boots may be slippery on hard tiles like this.

The most slip-resistant tile in the Swisstrax Garage Tile line is the Ribtrax Tiles. These are vented tiles and would allow water to flow through the tiles. Diamondtrax is also slip-resistant due to the pattern. Vinyltrax would be the only floor that would be quite slippery when wet. If you are wanting to walk over these tiles with ski boots, we would recommend using a rubber flooring surface. We do offer a rubberized version of the Ribtrax Tiles. Our 3/4" Endurance Rubber Tiles are the same as the Ribtrax Tiles in the standard version and the smooth version. The only thing is that they come in one color, Black.