Ok fair enough, I see what you are getting at now. @Marce might be the best to answer that on this forum
There are two rugby clubs with Army background: Liceo Naval and Centro Naval
Centro Naval, is an Argentine sports and social club, established in 1882 by a group of Argentine Navy officers. The rugby union team currently plays in Primera C, the fourth division of the URBA league system.
Centro de Graduados del Liceo Naval Militar, or simply Liceo Naval, is an Argentine sports club formed by graduates from Liceo Naval "Almirante Brown" (Almirante Brown Naval High School), one of the two educative institutions of the Argentine Navy. The field is located in Núñez, Buenos Aires, close to the Ciudad Universitaria.
But TBH there's no a direct link between UAR (Argentinian Rugby Union) and the Mounted Grenadiers Regiment. It's just like the Indigenous stuff with RA. The last Indigenous player was Kurtley Beale, oh, Dylan Pietsch now but Kurtley was the last starter and star in the team. It's not a full Indigenous team as an outsider could think about a team with Indigenous design is full of Indigenous players