Can I use antigen in gel to immunize rabbits to generate polyclonal antibody.

Yes, you can.

A standard PAGE gel will work. It can be lightly stained to locate the protein band, then de-stained and washed well with water. If you can send the whole band with an approximation of the protein content, we can aliquot it appropriately. Sometimes people send the band mashed up, it still works, but it's more difficult to aliquot.