I don’t recall anyone actually seeing the Romulans in Enterprise. They might have seen the Remans though.
Had the show gotten a few more seasons, I fully expected a Romulan War arc, and if Archer and the gang actually saw any Romulans, made a pact never to tell anyone and alter the logs to preserve the relationship with Vulcans. The late third season story with the Xenophobic faction on Earth being a factor in that.