I assume when he came in as a pinch runner, Gilbert was subbed as the catcher and had to bat for Skelton or be lost for game. Is that right experts?
No, that is not correct. Anderson could have batted. But I assume Henderson wanted to get Gilbert an AB in case he decides to start Gilbert at some point in this CWS.
How does the communication with the ump go in those situations? Is Anderson inserted as the catcher when he replaces Skelton on base and then Gilbert replaces Anderson as the catcher when Skelton's spot comes back up? Or is he called a pinch runner when he reports into the game?
Anderson subbed into the 8th spot in the lineup. Skelton is done. Anderson stays there until he is subbed out. That spot happened to be filled by a catcher, but that doesn't matter to the umpire (save moving a position player to pitcher and, thus, losing the DH). Anderson could've gone to any position in the field.
When the 8 spot came back up, Gilbert subbed in to hit for Anderson. Anderson is done. Gilbert remains in and plays catcher.
The only conversation that happened was likely "number x in for number x."
Maroon and White Basketball
Sam Purcell praises Mississippi State's offensive breakout: "The way they played at UT Martin was what I've been seeing in practice"
Maroon and White Football
Mississippi State Week 11 Preview: Auburn Players to Know
Rivals Football Recruiting
JUCO Intel: Top recruits taking mid-week, final officials before decision time
Maroon and White
Mississippi State S Kendel Dolby speaks on defensive adjustments ahead of Auburn game
Maroon and White Basketball
"His part in our team, no coach can do": Josh Hubbard impact felt on the court and in the locker room as much as in the record books