Both are co-developed by Vitei, the Japanese studio founded by British developer Giles Goddard. Goddard found fame as one of the first western coders to be welcomed into NCL's hallowed halls, but his relationship with the company goes back to when he was employed by UK studio Argonaut, which not only created the Super FX chip that powered Star Fox on the SNES, but also helped with the production of the game itself.
Given this information, it should perhaps come as no surprise to see Peppy Hare feature in Steel Diver: Sub Wars:
This could be an innocent cameo, but it has predictably led some fans to hypothoise that Steel Diver: Sub Wars takes place in the same fictional universe as the Star Fox series. That could be seen as some pretty wild speculation, but how else does one explain the presence of a talking rabbit? Share your own thoughts on this with a comment below.