As far as I know, no it does not stack. In order to compensate for that the feat progression of undead slayer incorporates some feats to assist with turning undead more effectively.
First, you get the sun domain at level 1. The sun domain has 2 bonuses to turning:
Exceptional Turning:
1. It adds a 1d6 to the total number of creature hit dice affected in the following formula (2d6 + base class level (cleric lvl or paladin lvl -2) + CHA modifier + 1d6 (sun)).
2. It also adds 1d4 to the "turn level" formula (1d20 + CHA modifier + 1d4 (sun)) to find the maximum level of undead you can slay based on your cleric/paladin base class level.
Also, at level 3 of undead slayer you get the Extra Turning feat which adds 6 additional turning attempts per day.