There is a FLAC player app I've seen on Head-Fi, but really in terms of functional usage, I'd just convert to ALAC. Converting FLAC tracks with something like XLD (you just have the output settings as Apple Lossless in XLD, then batch-open the FLAC files and it converts them into the same folder) takes a few seconds per track and is what I do with any FLAC stuff I have left from using Windows before I switched to Mac, or free FLAC downloads online. Lossless is lossless so you lose no data or fidelity switching between lossless compression formats.