Why are ya'll assuming that this is bad for Guts & Co? So far the Kushan haven't harmed a single person on the boat. Even if Guts is chained up (and I see no proof that he is, just that he is on his feet again), is that necessarily a bad thing? Maybe they just want to restrain him until they can be sure Rickert can talk to him and calm him down, lest he murders them all because he can't tell that they're friend and not foe?
I mean yeah the way they boarded the ship wasn't exactly nice, but I think it's obvious that Rickert has been searching for Guts. If they don't know which boat Guts & Co are on, they could easily be walking onto an enemy ship and into a fight. Much better to subdue everyone first, then check to see if Guts or his companions are among them, especially if they are trying to keep Rickert safe. It's not exactly a secret that he has a huge target on his back now, after openly defying and running out on Griffith.
Even before they showed Rickert I wondered if he was directing them to search for Guts. We know he got away with the Bakiraka, and Roderick's crew mentioned that the Kushan seemed much more efficient this time, which was a clue that Rickert was helping them. Rickert is a talented weaponsmith and one of only three people who knew Griffith personally at this point (four if you count Charlotte which I do not - she is infatuated with him but I don't believe she ever knew the real Griffith); he's an absolute VIP to them, and if he told them of a powerful ally who hates Griffith even more than they do (and Silat could back him up here), of course they'd want to find him. It seemed pretty obvious to me that they were told to look for a man with a giant sword and to be careful until they could get Rickert safely on board to talk to him. Guts was pretty helpless in this chapter; if they wanted to eliminate him they could have easily killed him before he had a chance to do anything.
Maybe the Kushan will have some magic that can help him master the Berserker armor, or at least know some way to expose Griffith as not human or make him corporeal so Guts can land a hit on him. The dervish who helped Rickert get away clearly had a few tricks up his sleeve that Griffith wasn't aware of. But in any case I think this is a reunion that has been a long time coming.