At second level Master of Shrouds (LM p46) gets Summon Undead ability:
Summon Undead (Sp):At 2nd level and higher, a master of shrouds can summon one or more incorporeal undead creatures a number of times per day equal to 3 + her Charisma modifier (minimum 1). This ability is otherwise identical to the summon monsterspells, except that a master of shrouds adds her Charisma modifier (if positive) to the duration of the effect.
At 2nd level, a master of shrouds can summon a single shadow. At 4th level, she can summon one wraith or two shadows. At 6th level, she can summon one spectre, two wraiths, or four shadows. At 8th level, she can summon one greater shadow, two spectres, four wraiths, or four shadows. At 10th level, she can summon one dread wraith, two greater shadows, four spectres, four wraiths, or four shadows.
What is the caster level of Summon Undead ability? What is its spell level?
Given no rules clarification, I'll probably rule that it is equal to divine caster level, but I'm primarily interested in rules' viewpoint. As for spell level, 1 + 1 per 2 levels of Master of Shrouds seems a good idea.