Loki is more likely to be an ally than a crewmate. However, he may feel indebted to Luffy after the Elbaph arc ends. In their first interaction, Loki attempted to strike a deal with Luffy by offering to eliminate a rival pirate crew in return for his freedom. The Blackbeard Pirates are Luffy's greatest pirate rivals. We all know the theories about Blackbeard gaining a third DF, particularly a Zoan, to complete his set. The legendary Devil Fruit of Elbaph that Loki ate, which is likely the mythical Fenrir, fits perfectly with that theory.
Both Loki and Blackbeard look up to Xebec, with Blackbeard even following his footsteps by becoming the ruler of Hachinosu. Blackbeard also named his main ship "Saber of Xebec." They share his dream to be the King of the World. Only one man's dream will continue. Blackbeard will defeat the false Sun God before facing the real one.