If you simply mulched with wood chips, there's no need to worry about N immobilization. I'm scheduled to have my entire front garden mulched with 4" of arborist's wood chips yet this week, something I do about every 3 years with absolutely no indication of nitrogen deficiencies.
Neither the worm castings nor the compost would do anything to mitigate any N immobilization, even if it did happen to be an issue.
Even if the compost was far from finished, I wouldn't worry about N immobilization as long as the compost isn't incorporated.
Al