Those are definetly engineers. This is a picture of the 9th engineers, odds are they gave them coats to look unique.
Also the guns they were using seemed way too small to be rifles. At first I though they might be using grease guns, but they were all only firing one shot at a time. I think the engineers are armed with Colt M1911 pistols. It would definetly make them more unique.
Aww, but they're wearing the brown winter coats in the summer, that makes no sense. C'mon Relic, if this is true then that's pretty dumb. There were/are other ways of making engineers stand out without giving them winter coats.
And btw a lot of US infantrymen wore those coats during winter, not just engineers.