The descriptions for the Reboot, Assimilate and Overload achievements all state "hostile robot", but I was able to get all of them by hacking a neutral (green) bot (a serf). Maybe this is intended but I thought it would be a bit harder if I had to hack an actually hostile bot.
Yes this is intended. It wasn't limited because the entire system is being replaced in future versions anyway. (That said, these particular achievements are just for teaching/using mechanics rather than actual "accomplishments," so these and a number of others are not actually limited despite their descriptions. You'll find other similar examples.)
I'd like to add that recently the word "hostile" in achievement descriptions caused some confusion where players thought the "win after destroying 400 hostiles" achievements and the like worked like the above mentioned achievements, i.e. destroying neutrals counted towards them.
IMO there needs to be a distinction in these descriptions.
"hostiles" vs "non-friendly robots" or
"hostiles" vs "hostiles and neutrals"
As mentioned above this was as special case. "Hostiles" doesn't normally include neutral bots, only anything actively hostile to you.
Those achievements in particular will be adjusted later since the entire hacking system has been replaced. Regardless, I'll update them earlier rather than later to avoid confusion since there's no telling how long it'll be before we get the actual hacking achievement list.