Looks like a tick or a mite to me - might just be one of those harmless paper mites but I'd give the tackroom a good dust, vacuum, and spray, and wash the rugs just to be sure (you could add some insecticide to the first wash then wash again to rinse). Pyrethrin-based insecticide would be best, it's harmless to horses and humans (toxic to fish and invertebrates only).
ETA: The Evil Horse of Doom can't spell "rinse" today... Posted via Mobile Device
Just had a closer look at the photo - you're right, it's not a tick because ticks are arachnids and this thing has only 6 legs. I'd be betting some kind of louse then. Too big to be the sort that lives in your hair but there are heaps of species and I'm pretty sure they're all parasites. Posted via Mobile Device