Bitcoin exchanges are far too slow for actual "high-frequency trading". For regular HFT, milliseconds may matter, while on most cryptocurrency exchanges you're lucky if you can get a response within half a second for placing an order. Fetching things like the order book often takes longer and many exchanges have tight limits on how often you can query the API.
HFT just refers to taking advantage of a timing difference for profit.
If you move your VPS closer to a Cryptsy server for the purposes of getting updates sooner, technically you are dealing with a HFT environment.
No much, but still.
The only difference between Cryptsy and NASDAQ servers is Jersey.
Both are Linux
Both use socket technology
Both do the same job.