Did Dignaga argue against real relations? Did Dignaga argue against real relations? I gather that his student, Dharmakirti, did.

I'm asking only because I'd disagree, but am skeptical about universals.
DharmaKirti and Dignaga are highly revered in Tibetan Buddhism and their work is used as foundational materials in Tibetan Buddhist monasteries to this day including the famous Sera Jey Monastery. However, they are also considered to have espoused or based their work on either the Yogachara tenet system, the Sautrantika tenet system or some combination thereof.

In brief, Yogachara/Chittamatra is a tenet system of the Madhyamaka and the Mahayana which believes in the selflessness of persons and selflessness of phenomena, but also believes in true existence which is refuted by the Prasangika-Madhyamaka. The Sautrantikas in general did not posit the selflessness of phenomena and are a tenet system strictly associated with the Fundamental Vehicle (like modern Theravada) as opposed to the Mahayana.

So if by "real relations" you mean "true existence", then I think both Dignaga and Dharmakirti posited real relations. If by "real relations" you mean "inherent existence", then I think both refuted real relations.

However, perhaps it is best if you elucidate what you mean by real relations and/or universals otherwise it is very easy in my experience to misunderstand one another. In my experience, when discussing tenet systems precision of language is key and knowing the jargon is very important even if difficult. I'm still struggling with it :)