I checked out the Brother QL-720NW as it has AirPrint built in and some people have that working with Go. Brother has a Raster image developer paper. Not sure if this would be useful in sending the FileMaker rasterimages to the printer directly, if this is possible at all, or if this is possible from FM Go.
I want to be able to skip the iOS print dialouges. I understand this is an option at some enterprise level of iOS development but not available for anything offered publicly through iTunes. Remote scripting a FMP robot to print the labels sounds like the answer unless someone has a better idea.
Brother looks to be a faster printing and better built machine with built in cutter and support of b/g/n wifi. Dymo has more die cut label options, nice. Zebra seems more proprietary and clunky in many ways with limited wireless machine options in a small size. I might just buy one to see if it works. They are not too expensive.