If they'd moved there since the 2014 invasion I would agree a small %, could be sleepers.I know it sounds very John Le Carre, but It wouldn’t surprise me if some of them had moved to Russia several years ago to wait and prepare for days like these - ‘sleepers’.
But prior to 2014... I'm more doubtful. My (albeit limited, family focused) interactions with Ukrainians from 2009 to 2013...they easily referred to their 'Russian brothers and sisters '. Could just be my narrow experience though.