This could be explained in lore:
Saphir says in the second SBC dialogue that half the recruits served the White Mantle in some way, so they could have brought the gear along with them (it isn't like the Blade have the resources at their disposal that the Mantle have.)
Also, it is much easier to hide a flag than it is to hide a symbol on a weapons rack. what perfect camouflage than to have enemy symbols around your base to deceive them that you are on their side?
And yeah, as Konig said, it is more game resource re-use than lore fail. On the other hand, they could have used resources from elsewhere (Drok's, AC, as 2 examples) but using these could actually be a smart move