Shanks have same Fighting Style as Roger, and apparently Shanks Fights with a Flaming Sword
If that's the Case, then Roger probably can also make his Sword covered in Flames
(I mean if Luffy have a Flaming Attack, and so does Shanks, and Roger's Son who is Named after his Sword have Fire Powers, then Roger probably Fought with a Flaming Sword as well)
This suggests that Man With Burn Scar is Someone who once Fought Roger, just like We previously had Kaidou who was given a Scar by Oden, Roger should have such Foe as well, and it's probably Xebec (Who Oda made sure to show us that He is a Forgotten Pirate, only Oldies Remember him)
If this Man With Burn Scar Crew is Captained by Someone Defeated by Roger (Whirlpool Ability indicates He have Davy Jones-Like Powers)
Then imo it makes sense that He will have a Crew Member who was Defeated by Ace, Someone who also lost his Fearsome Reputation, and as i said before, it could probably be User of Vampire DF (Patrick Redfield)
So if this Crew is made up of Disgraced Top Tiers, who would it make sense They'd recruit? Kid ofc, that's why Oda made Kid look for him.
And who else? Moria, Magellan, Weevil ... etc
Basically Captain Defeated by Roger, Commanders each Defeated by Someone Super Famous, Moria Defeated by Luffy, Magellan Defeated by Blackbeard, Weevil Defeated by Marines, Kid Defeated Shanks, maybe Shiki Defeated by Garp/Sengoku ... etc
A Crew Made-Up of Davy Jones-Like Captain, Poison Demon, Dracula, Frankenstein Monster, Zombie Man, Iron Monster ... etc
Basically Nightmarish Crew which fits their Theme as a Black-Only Ship that doesn't leave any Witnesses