There are more than 27 uniformed from what I have counted. But only 27 are active. Historically, UT has several guys on the trip that Vitello typically feels is important to gain the experience of being there as he plans for the future and the future roles of several guys on the team.
Most of the extras were released before regionals to play summer ball. As far as pitchers, as mentioned, Dallas and Schaefer are not in Omaha. Others, like Hunley and maybe one other, are there and dressed in the dugout. A few extra position guys are there as well, etc.