There is nothing in the Pennsylvania Workers' Compensation Act which would prohibit an injured worker from applying for unemployment compensation benefits after a case is settled by Compromise & Release. There may be an issue with qualifying for unemployment compensation benefits however. You must be able and willing to work to be eligible for unemployment compensation (you cannot be totally disabled). Also, in many settlements, a resignation is required as part of the deal. This may make you ineligible for unemployment compensation. These are issues you should discuss with an attorney prior to settling, so you can know your options.
Resignation is often part and parcel to receiving a settlement. In addition, in order to be eligible for unemployment, you must show that there is no work available to you. The employer hasn't necessarily terminated your position simply because they are settling your case. I think you would be hard pressed to get UC benefits after a WC settlement.
You can apply for unemployment benefits now and if you did not agree to a resignation as part of your settlement that employer plans on submitting to O.E.S., you are "willing and able to work" (i.e., have "reasonable" medical restrictions that don't place you out of a significant portion of labor market); have worked recently and long enough to qualify you should be awarded unemployment benefits. Again, assuming they don't ask for a resignation, they will continue after the settlement hearing. There will be a credit against you weekly workers' compenation (minor economic loss to you vs. knowing if you quailfy) until your settlement is paid. In other words, you can't get both the full amount of Worker's compensation and Unemployment at the same time. There is an "offset", one against the other. To avoid offset you can wait until after the settlement hearing, but you will not definely know if you are entitled to unemployment benefits at the time of the hearing unless you previously applied and have an O.E.S. determination. Many of my clients wait and are awarded unemployment benefits. Some are denied depending on information provided to O.E.S. by the employer.