Jawsome I'm not too familiar with the ins and outs of crossover deals, but I think IDW would probably take the initiative and do all the leg work like they (I assume) did with the Stranger Things crossover. It was IDW's people who worked on and promoted that series. IDW's people/connections did the art, editing, lettering, design, almost everything. It seemed Dark Horse was co-publisher basically only in name only.
So if IDW is willing to do all the work, and it's just free money for the other publisher, I don't see why Dynamite wouldn't also agree to a deal like that.