Of other current Ent-E personnel original to the books, assistant CMO Dr. Tropp and transporter chief T'Bonz debuted in A Time to Sow by Dayton Ward & Kevin Dilmore. I think Glinn Dygan was created by Una McCormack for Brinkmanship, and Aneta Šmrhová was created by Dave for Cold Equations.
Dygan was established in DRGIII's
Plagues of Night, though he doesn't do too much there. Given the amount of development he is given in
Brinkmanship, it wouldn't surprise me if DRGIII and
Una McCormack shared notes as he was writing
PoN, nor would it surprise me if his character's genesis ultimately did rest with Una.
But that's speculation on my part. You are in a better position to know than I,
Christopher. In any case, Dygan was first established in
Plagues of Night, released in May 2012, but was significantly developed in
Brinkmanship, released that September.
Aneta Šmrhová was created by Dave for Cold Equations.
The earliest appearance by Šmrhová I can think of is Destiny, actually. Although could she have been in
A Time to Kill and
Heal too? I really liked David's recurring security and operations people that seemed to begin then and carry into
Destiny (Alas for that runabout crew that got massacred in the 3rd Cold Equations book seemed to include several...)
.
Šmrhová is definitely in
Destiny. Memory Beta doesn't list her appearing any earlier, and I don't recall her in the
A Time To... books that Mack wrote. (Which makes sense– she's a nice foil to Choudhury, but would not, I think have been that interesting alongside Vale.)