Backlash is Tank #1 for Alpha, and he has been in the Ghost Corps for just under 12 years, so he will definitely know Tesla. He's generally a good soldier too, which means he'll like her work ethic, though he might be a bit more troublemaking than she is. He's pretty attached to his team members, especially those who have been around as long as or longer than him. Definitely friends, maybe with a we're-basically-family vibe?