SL and TP orders held at Oanda server ?

Are SL and TP orders held at Oanda server's ?

Yes, at least mine have been actived while my computer was shutdown.
Is it what you wanted to know ?

Yes, thanks , how reliable are those orders executed ?

They are somehow too reliable because during newstime or weekends, the spread widens by A LOT (10 pips or more) and that can take out your stop-loss while the price won't be hit on the chart. It's logical but it can be unsettling.

There is another case : on mondays, especially on GBP/USD, there are often gaps on the price that jump beyond your stop-loss/take profit and they don't get actived. It never happened to me because I'm an intraday trader and I never heard a complaint about that with an Oanda client but I know it can happen and I wouldn't rule it out with Oanda.