I don't know what they are. It is possible they hex-edited the original rigging.dll, similar to what the New Horizons modders did. If they are duplicate rigging object .dlls, Maelstrom provides two solutions that were provided. The reason NH needed to hex-edit multiple rigging.dll files is because they wanted separate flag textures, because the original game only allowed a single row of flags in the texture file; Maelstrom now allows many rows and to see how that works, see the ERAS RESOURCE\Textures\flagall_ship.new.tga.tx, RESOURCE\INI\rigging.ini and Program\battle_interface\BattleInterface.c function procGetRiggingData.
New Horizons could use that same technique, but the quicker way, so that their textures and script code can remain mostly the same, was Maelstrom added a feature to give an alias to various rigging instances within the script code. You can see this in the Maelstrom New Horizons version that I edited PROGRAM\SEA_AI\AIShip.c, where there is an option to add a unique .iniSection and .lblGroup to the flag objects to indicate what locator group on the ship model to use, and the iniSection refers to configuration sections for different .tga.tx files to use for that name, which you can see an example in the Maelstrom New Horizons RESOURCE\INI\rigging.ini file. This allows them to still use the multiple flag textures, but with just one rigging.dll because it will accomplish the same thing their hex-edited .dll files with these new features I added just so that it could work similarly, without the need for additional hex-edited .dll files.
If the personalflag.dll and questflag.dll are not used for ship flags like New Horizons, then I do not know what they do in their mod, so I can't answer the question.