However that article speculate why Marvel withdrew their attempt to challenge the rights claim of IDW but doesn't know why.
Well there is a commercial for the ROM toy where the narrator mentions that ROM's enemy is the DIRE WRAITHS. Also I think the old toy package mentions the Dire Wraiths also.
Marvel did design the Wraiths in terms of appearance and powers, but IDW has their own unique look for them and same or similar powers.
But I would guess that since the old commercial mentions the Wraiths by name that they are in some way linked to the ROM trademark, so if IDW has ROM then they should get the Wraiths as well.
The commercial that mentions the Wraiths is here:
Interesting. I guess it depends on how the contracts were written, of how much created in the comics belongs to Hasbro vs. Marvel. However, trademarks have to be used. There was more than ten years between Marvel's Rom series and IDW's, so as a trademark, it was up for grabs, anyone could have used the name "Dire Wraiths" for their own villains as long as they weren't similar to the Rom villains in execution. The question then becomes, was there enough in packaging and the commercial for Hasbro to lay claim to the copyrights of the actual story that Marvel developed? You cannot copyright just a name. That Marvel has referenced other things that were developed for the Hasbro titles from outside the actual toys (Bug, Marionette of Micronauts, the human version of Rom and the other Galadorian space knights), I would think they would have a pretty strong case if they wanted to pursue it.
But, there's not much they could do with the Dire Wraiths that they couldn't already do with the Space Phantoms and Skrulls anyway. So, I could see why they would just let it go.