That was Sheridan. Sinclair was season 1, then faffed off to go run the Rangers and become Valen.
There's a whole string of Babylon 5 stuff. In Operation Klondike we are also treated with Star Captain Brucalter Sheridan leading the attack on Babylon in the section called "Sheridan's Battle". Of course, it was
Bruce Boxleitner playing John
Sheridan way back when, just a tad too convenient to be a coincidence?
Also, I remember reading through Field Manual Comstar the first time, spotting all those units named after B5 episodes...
For non-B5 references, I have always liked the 33rd Scorpion Grenadiers (Sharman's Boxers) entry, with references to Australian band Midnight Oil and a certain song by them!