(Editor’s note: I completely forgot to do this analysis in 2018; this is all back-filled):
Here’s the announcement of NRIs: https://www.mlb.com/nationals/news/nationals-annouce-2018-non-roster-invitees/c-266367066
Confirmed by https://en.wikipedia.org/wiki/2018_Washington_Nationals_season .
RHP
Brady Dragmire
David Goforth
Edwin Jackson
Jaron Long
Roman Mendez
Chris Smith
Cesar Vargas
LHP
Tim Collins
Ismael Guillon
Bryan Harper
Tommy Milone
C
Miguel Montero
Jhonatan Solano
INF
Reid Brignac
Chris Dominguez
OF
Ryan Raburn
Moises Sierra
Additionally, the Nationals have extended invitations to Major League Spring Training to the following four Minor League players:
RHP
Jimmy Cordero
C
Taylor Gushue
Spencer Kieboom
INF
Osvaldo Abreu
Did any NRIs make the 25-man roster out of spring? Yes: Miguel Montero, who played four games (4), then was released. Money well spent.
Did any of these NRIs appear for the Nats throughout the 2018 season? Yes, Montero, Collins, Sierra, Cordero, Kieboom.
Special Mention: Edwin Jackson did not appear for the Nats, but he did secure his ML release then ended up being quite productive for Oakland later in the 2018 season.