The Paladin module won't work for Alliance Paladins.
Code:
local Dot = GetSpellInfo(53742) or GetSpellInfo(31803)
That code will always return Blood Corruption. When you call GSI with a spellId you will always get return values.
Code:
local Dot = GetSpellInfo(GetSpellInfo(53736)) and GetSpellInfo(53742) or GetSpellInfo(31803)
That should work to actually switch to Holy Vengeance on Alliance Paladins.
Basically you query to see if the Paladin has Seal of Corruption in their spell book by getting the localized name of the seal with the inner GSI call. The outer call uses the name, if Seal of Corruption is in the player's spell book the function returns non-nil which then sets Dot to Blood Corruption. Otherwise Dot is set to Holy Vengeance.
I know this works for Alliance, but can't test for Horde.