If they have been able to avoid detection, survive the inhospitable climate, managed to take a Triarian down before he even noticed they were there (A second is too long, due to the telepathic link, to remain completely unknown) then managed to move the Triarian and keep him alive returning him to stasis (They live on worlds with temperatures in excess of 400 Celsius) then ensure he cant even have a second awake and loose (They manipulate energy, you don't want that loose) while avoiding the big brother surveillance and dodging Triarian space security (In their main, relatively physiologically consistent form, they were made by the Aetherii and were existing within the Aetherii until their devolution, after which they spent just over a thousand years returning to space faring status) then yes. Just know the majority captured will be those from the interlude years due to that having been the easiest time to capture them (The period between devolution and space faring status)