No, an employee on sick leave is not accumulating holiday entitlements.
Where the employee had worked 117 hours in the calendar month before / after sick leave, he would still be entitled to 1/12 of his annual leave for that month.
If he worked less than 117 hours, he is entitled to 8% of the hours worked.
Once the employee has worked over 1365 hours in the annual leave year, (in the same employment) he is entitled to 4 working weeks holiday. I think this can still be achieved working 8 months of 40 hour weeks.