Was Ricimer present at the battle of the Catalaunian Plains?

[Flavivs Aetivs]

was it possible that Ricimer was there? Or do we at least know for sure that he wasn't?

It's possible, I suppose - but you're right that we don't know very much about it! Majorian almost certainly was not there, Ricimer may have been, but his career prior to the fall of Petronius Maximus is largely a mystery.

In my book I state that the fact that Sidonius doesn't mention any involvement at the Catalaunian Fields in Majorian's Panegyric, especially considering Sidonius himself probably accompanied Avitus to at least Aurelianum, is pretty significant evidence that he wasn't there and had already been replaced by Agrippinus.