As someone who's done it, yes you can still claim a tax offset for any out of pocket medical expenses over $1500 even if you've qualified for, and are receiving rebates from, the safety net. I kept everything, all my receipts for anything medical related for the entire year and got my 20% back on that. Even if you haven't got receipts, call your clinic and get them re-sent to you. They get those sorts of requests all the time.