If the US has the right to seize the oligarch’s yacht, then I suppose it can seize whatever it finds on it. I doubt it’s a real Faberge Egg, but you never know.
It may be a copy and it would seem a bit risky to take something like that on a yacht, but Andrey Melnichenko apparently has three Monets on his yacht.
Apart from that, Viktor Vekselberg, whose yacht was Seized by Spain at the request of the United States owns ten eggs, although most of them are in the museum in St Petersburg.