A common criticism of unions is that they work to increase pay and benefits for their members who are established employees at the expense of those who are looking for work. It seems to me that there is the same conflict between the employed and unemployed in the co-op economy, where established worker co-op members have powerful incentives to prevent new entrants to their field from driving down their profits and bargaining power. As a career changer myself, I am interested in knowing how one would balance the needs of the unemployed or underemployed against the interests of co-op members with established careers and undoubtedly much power over hiring decisions.
Unemployment is a basic irrationality that is and always has been intrinsic to capitalism. Neither slavery nor feudalism nor other systems exhibited it. Unemployment exists because employment depends on capitalists' ability to profit from it; if profit opportunities dictate unemployment it happens. In a worker coop economy, the blatant irrationality of unemployment would likely be more widely grasped. Unemployed people continue to eat, dress, inhabit dwellings, etc.; in short they consume while not also producing. The society is unambiguously better off if such folk were kept employed to share their output with the output of others that they consume. The likely ways to achieve no unemployment would be (1) to reduce the work hours of the employed and thereby absorb the unemployed, (2) poll the population to see what needs to be done and employ the unemployed to do that, and so on. Since profits need not and would not be the bottom line, the basic driver of a worker coop-based economic system, profits would not dictate behavior and thus the result of unemployment. In direct response to your question, if unemployed who already consume are employed, there is a net addition to output so that the employed need not and would not suffer any loss of benefits or wages from ending unemployment as indicated.