Here's the relevant paragraph from the means assessment guidelines for disability allowance. Net earnings are assessed.
Net earnings are gross earnings less income tax, PRSI, Superannuation/PRSA contributions, union dues and reasonable travel expenses.
Not all income is assessed. The first €120 is disregarded, along with half of net earnings between €120 and €350 pw. Anything over €350 is assessed in full.
Work must be of a rehabilitative nature to qualify for the disregards, and you should advise the scheme area before you take up employment.