That's ultimately the prospective employee's call to make -- they either want the job enough to sign the contract, or they don't.

If there's an underlying concern on the part of the employee in relation to patent or copyright to something they have created, are creating, or hope to create on the side, they may want to discuss those concerns with the employer beforehand in order to ensure that the employer won't be making any claims. If the employer won't make such a commitment, we're back to how badly the prospective employee wants the job.