The unglazed tiles are pretty much the same as the glazed tile, except that their surface is not coated. Unglazed tiles do not show wear because their color extends throughout the tile, making them ideal for commercial applications. Any tile that is frost resistant may be used outdoors. For safety reasons, only unglazed tiles with a slip resistant surface should be used on patios, walkways, pool decks, etc. Glazed tiles should only be used on vertical surfaces when used outdoors.
Tile is about as slippery as vinyl or wood.
Naturally, if the floor gets wet, any of these hard surfaced materials will become slippery. There are many tiles that have slip resistant surfaces but keep in mind, that the more abrasive the surface is, the more difficult it will be to maintain. You might consider using a mat in wet areas. Glazed tile should never be waxed. The purpose of the glaze is to give you a maintenance free floor.