short version:
pr_checkextension 0 should stop AD from using QSS's particle system.
The map itself will still use rain particles, but the dp effects should no longer be loaded.

long version:
QSS has a compat layer for DP particles. The fact that people here are saying that they look like DP's just goes to show that the compat layer is working, for better or worse.
Using the compat layer means more engines can have acceptable particles without having to redo the particles for every single engine out there (especially when Sock had initially created most of the effects for his earlier ITS mod, and with the extra AD effects still exclusively with DP in mind, and iiuc derived from SMC). Imho vs FTE/QSS's native particles, DP's lack things like spawn patterns resulting in a general puffiness to the effects; whereas FTE's particles do a decent enough approximation of both hexen2 or quake2's effects (or at least the ones I implemented).
The puffiness is then compounded by the use of pointparticles instead of eg .emiteffectnum, which bloats the networking and gives bursts of particles rather than a more continuous stream. Again, DP compat...

The QSS engine has absolutely no new particle effects built in. ALL new effects are being read from some mod-specific file. The only particles from me specifically are the ones inside the fte_weather.cfg file, which are basically just rain+snow effects.
The r_particledesc cvar says which effects the engine tries to automatically load (defaulting to some 'classic' placeholder).
However, AD then detects support and uses the whole namespaces thing and in doing so forces the engine to load additional effects (which take precedence over the classic effects) while also suppressing the mod's own fallbacks.
If you want to disable the particles, either tweak world.qc to prevent the mod from detecting FTE_SV_POINTPARTICLES, or hack the engine to not advertise it
Note that pr_checkextension 0 will prevent ALL qc extensions from being advertised, thankfully AD still doesn't depend on any extensions thanks to vanilla QS. However, I'm not going to add that option to any menus because it would break mods that depend upon (other) extensions. The choice of whether to use extensions or not MUST be made by the mod, not the engine, anything else is hacky/flawed. Presumably this would be best done using cvars thanks to QSS supporting the set/seta console commands (or possibly just another unreadable temp1 bit).

@Barnak: waves like http://triptohell.info/moodles/junk/fte00040.jpg ?