"Enchanting"?
Do you mean "Enhancing" (as in, adding gold, spined leather or a wood color, depending on type and composition of the item)?
No, it doesn't count as two slots for the luck; though 190 luck will take up 190 of the 400-600 points that an items properties can take.
But, remember that enhancing for luck will add more than one property to an item for most items.
Gold on metal weapons adds 40 luck, but also 30% Lower Requirements
Gold on metal armor & shields adds 40 luck, 30% Lower Requirements, and resists.
Spined on leather armor types adds 40 luck, and a lot of physical resist.
Bloodwood adds 2 HPR and 40 Luck to wooden shields.
Oak adds 40 luck to wood weapons and armor (and resists to armor), can't remember if it adds something else to the weapon.
Heartwood, IIRC, has a random chance for a 40 luck result - but still adds resists to armor & shields.
As all items, even at maximum skill with enhancers like the ancient smith hammer +60, reach the point of 100% failure in enhancing from luck in the 130s if not earlier (different points for different items), you have to use a forged metal tool to enhance a 150 luck item to 190 (which costs real money to buy the tool from the in-game store via sovereigns). You should NEVER enhance before imbuing to the item's max, as properties added in the enhancement will go ON TOP of the imbued stuff if done last, but will limit your options if done earlier, as all the added amounts count toward imbuing strength.