Missile launch warning detectors + flares (the OV-10G+ appears to have both, from publicly available photos) have proven quite effective against MANPADS. Turboprop exhausts at the edge of the missile's envelope (10,000-15,000 ft slant range) are not a huge target.
Other differences since the last time anyone used an OV-10 in combat include much better EO/IR sensors and digital map displays, which do a lot for SA at altitudes above the golden-BB (and even medium-cal AAA) range.
It also has two crew, both with a good view and the Mk 1 eyeball's wide-angle coverage, rather than being confined to the soda-straw EO picture, and it doesn't rely on a satellite link.