It kind of makes sense that a general purpose droid like a Treadwell would be junked in an industrial community like Cloud City (there would be lots of them and eventually they would wear down beyond the point of economically viable repair).
Equally a place like Cloud City would get alot of visitors who's ships may need repairing and having a starship wall panel recycled sort of fits.
But it's a bit odd that they would have a couple of battle droids there (it's not an military site, it's not a bounty hunter's den like Jabba's Palace, a good case could be made for swapping some of the droids in EV-9D9's torture chamber for the battle droids here).
As I said before it's not as annoying as seeing the medical droids sitting in on the Rebel Briefing but it does feel a bit odd.
I suppose it could be argued that the IG droid and the 4-LOM looky-likey aren't battle droids and the the bounty hunters just modified a pre-existing model to serve their purposes.
And as the IG series are only identified as specifically built battledroids in the EU I guess it's easy to rationalise it in those terms.
IG-88 does look like a hard arsed piece of military kit though (much more than the battledroids in the PT do), I can't really visualise it cutting lawns or cleaning windows.
It's only really a concern for people who have seen the film so many times that they notice stuff like this.