A hybridoma by definition and by the way it is generated produces only one type of antibody, i.e. a monoclonal antibody. It is unclear from your question whether you want to inject one hybridoma or several. In the first case you get an ascites with a monoclonal antibody, in the second case a mixture of several monoclonal antibodies, which does not equate with a polyclonal serum. Polyclonal sera are often made by injecting the antigen into rabbits or goats, then collecting the serum from blood samples.

In any case, making ascites is considered painful to mice, and would need a very good justification why it is preferable way of producing antibodies over in vitro cultivation of your hybridoma(s).