Whether I agree with your stance towards GDKP or not, the title of this post is whether we can mass report GDKP advertising.
GDKP in and of itself is not against any rules nor does it incite breaking any rules, and as such is not a violation or reportable act. What may be reportable though is advertising guild recruitment or raid recruitment in the /LookingForGroup channel which is apparently explicitly for group activities happening now.
This post has some replies with various links to blue posts, and documentation that gives some information/insight into how that may work, and why reporting posts to /LookingForGroup that are advertising GDKP runs at a later date/time may be appropriate (though, it may be noteworthy that this appears to have no correlation with the type of loot distribution system used for the run):