There seem to have been some Finnish volunteers on the "people's republics'" side a bit earlier as well but they obviously haven't been reported in international media. But I don't think the volunteers were the during the most active fighting and I don't think they number more than half a dozen at the most.
The Finnish language propagand..sorry information about their life and conditions has given the readers a very positive, outright homely picture of these brave warriors, stemming the tide of fascists coming to rob the poor Novorussians of whatever it is they are entitled to. These heroes, having been issued decorations even before rifles, have also been active in outright heroic bravery and one even managed to get slightly wounded by (according to the published bulĺsh...sorry propagand...nonono I mean information he was shocked to be shot at during ceasefire while peacefully being on sentry duty with his peace-loving rifle).