Very tentative proof if any so far. It's 2 videos both with low flying A-10s doing nothing. Could be recycled footage, could be current air patrols. No images of anything damaged by US.
It's also strange to fly so low when we know Syrian government and even many of the rebels have MANPADS. Makes me think this is peacetime/flying over friendlies.
I don't think US affords the domestic or foreign image hit they would incur from openly fighting the Syrian government. Russia is salivating over the prospect killing some American pilots, and the skies are very much locked down by their air/air defenses.
How would US government explain to the world and their own public that Russia shot down their planes that were helping ISIS? Same ISIS that were beheading US PoWs years ago btw.