Just from a quick test, both the Reaper and the DF break the Onslaught's armor, dealing around 2600 armor damage. The reaper then deals ~1800 hull damage, while the DF deals ~600.
For the interaction with Damage Control - beam damage ticks happen 10 times a second, but the hull damage happens during the tail end of the beam when damage/second is lower, so chances are for the initial DF shot, Damage Control would not get triggered at all.
For a hit vs completely bare hull, the first tick would deal 800 damage, which gets reduced to 600 by Damage Control to begin with (and possibly further by e.g. high CR or Solar Shielding or anything else, such as residual armor), and subsequent ticks would not be affected if one of the ticks triggered it, so *at most* we're talking about the full hit losing 60 points of damage, and less than that in any sort of real scenario; basically negligible.