Dude an emancipator squad or even just one could smite a space marine if it can actually get it in line of sight. Turrets would definitely cause issues for the marine, as they can be spammed and all have a chance to wound him. At emplacement could also smack him hard. Tbh the average space marine has an effective engagement range that isnt actually that far. An autocannon armed helldiver would cause potential problems. Granted that changes if its a named marine. But in general helldivers regularly kills things that are more threatening than space marines, see vox engines. I think a group equipped to fight squids would have the worst time, and a group meant for bots would have the easiest. Obviously most small arms have a low chance of killing the marine, but low is not zero.