A brief update; a couple of items to highlight:
The OTA process is mostly solid. No more locking up of the board and rogue SMS's.
TonyM and I have seen, on isolated occasions, what appear to be incomplete OTA's. The OTA process starts, but the board does not restart (even after power cycle). Reprogramming via USB brings everything well again.
Theory: I've only noted this when running off USB power only (but it's a fairly strong little 2A brick). Given that I'm loading a rather large sketch (42k or so), perhaps we are working the modem a bit hard for many seconds in terms of amperage (again, no battery). Cell signal is weak when I've noted this occurance, somewhere around RSSI = 8. This behavior is the exception, not the rule, and I'll be trying soon with USB + battery to see if that helps. NOT a show-stopper by any means, but thought it worth sharing to make the Hologram team aware. I also recall the whole OTA system is likely to be overhauled, so again, not a show-stopper.
UPDATE 6/21/17: After a power cycle, the Dash will successfully accept a second OTA attempt. I'll also try with no power cycle -- i.e., two OTA's in a row, no power cycle in between if the first OTA doesn't take.
Update 6/21/17: Looks like it may even take a second OTA attempt (successfully) without a power cycle. Neat!