Your employer can definitely petition for your GC while you are on OPT. USCIS does not deny your GC petition just because your employer filed for it while you are on OPT (F1 visa). The main concern is the timing. If your OPT expires before you get EAD (from EAD/AP/i485 application) with pending i485, then you cannot continue working and need to leave US. You can also apply for H1 in the mean time while you are in the process of GC application.
If you are on 17 month OPT extension, you are in good position to go through EB processing. Whether your PERM or i140 is approved depends on whether you education/skills are suited for the job position. Your OPT status will not hamper in any decision making byUSCIS.