Please remember that WWOOFing is volunteer-based. It is not comparable to employment, and you are still required to search for a job.
If you decide to WWOOF while receiving unemployment, a few restrictions apply.
You are allowed to WWOOF, but it has to be during your time off. As you know, a job-seeker has the legal right to take some time off. It is limited to 35 days a year (a total of 5 weeks). You are allowed to leave for more than seven consecutive days, but you must let your agency know (on the Pôle Emploi website for instance). You will then be able to WWOOF without any issues.
Do not neglect this step; it is essential. As a matter of fact, not replying to a convening letter while being away with no justification has consequences. You could be automatically deregistered or merely lose your benefits.
One more thing: “Outside the box” experiences look good on a resume, do not forget to mention them!
Sources (in French):