http://www.citizensinformation.ie/en/employment/unemployment_and_redundancy/redundancy/redundancy.html
"Can I be made redundant if I am on sick leave?
If your employer decides to make you redundant while you are on sick leave, you may qualify to bring a claim for unfair dismissal. Unless your employer can prove there was a genuine redundancy situation and that fair procedures were followed, your dismissal may be found to be unfair. Even if a genuine redundancy situation exists, you may bring a claim for unfair dismissal if you consider that you were unfairly selected for redundancy. Your employer should apply selection criteria that are reasonable and are applied in a fair manner."
so it looks as tho the answer may be yes
however from what you say
that they have assessed him as understandard but never asked him to pull up his socks does mean he has a case
hmm - start a grievance I think
( on grounds that the matriz assessments do not match reality