Hatake Sakumo was referring to the Remnants of the ninja who had once served under Besa. After Hanzō took control of Amegakure Ninja Village, the former leader's subordinates became targets of a purge. Some had failed to escape, while others had sensed trouble early and fled. Though few in number, they remained a threat.
Previously, Hanzō had needed to reassure the neutral ninja in Amegakure Ninja Village and win them over, so he had not immediately sent anyone after the fugitives. Only once the situation settled down did he dispatch the Anbu. But those fugitives were also elite Amegakure Ninja who knew the terrain inside out, making them difficult to find in the short term.
Hanzō felt that these people would not give up so easily. They might attack the crucial medical ninja from Konoha Ninja Village when they came to treat the civilians. If they succeeded, even if Konoha Ninja Village knew Amegakure Ninja Village had not benefited from the attack behind the scenes, it could no longer send medical ninja to the Land of Rain.
After all, training an excellent medical ninja was an extremely demanding undertaking. Though Hanzō did not know the specifics of their training, comparing his own village's circumstances with Konoha Ninja Village's outstanding medical ninja gave him some sense of the effort Konoha had invested.
With Amegakure Ninja Village's current resources, it would take at least several decades to catch up to Konoha Ninja Village's level, and that was assuming its development proceeded smoothly. Thus, if anything happened to even a single medical ninja, Hanzō would have no way to answer to Konoha Ninja Village. He could not even compensate for the loss.
Hanzō ordered the Anbu to keep a close watch on the area around the Medical Unit and remain alert for any