OK, first of all you cannot scalp at Oanda. Scalping is market making, its getting inside the spread, its buying bids and selling offers. What you're talking about is micro time-frame trading. Semantics over.
I know lots of guys who grid with Oanda. (Its a miserable way of pretending to trade, so let's not get a flame-war about it, I'm just using it as an example.) Gridding, in fast markets, involves frequent trades, more accurately frequent buying and selling. They never experienced problems getting filled on their orders. There's also an Aussie who trades crazy (meaning very, very often, like 300 rt/day, if I remember correctly) at Oanda, and he seems to be able to get accurate fills. Altough I haven't seen him around for a year now.
So, the short answer to your question is NO.
I know lots of guys who grid with Oanda. (Its a miserable way of pretending to trade, so let's not get a flame-war about it, I'm just using it as an example.) Gridding, in fast markets, involves frequent trades, more accurately frequent buying and selling. They never experienced problems getting filled on their orders. There's also an Aussie who trades crazy (meaning very, very often, like 300 rt/day, if I remember correctly) at Oanda, and he seems to be able to get accurate fills. Altough I haven't seen him around for a year now.
So, the short answer to your question is NO.

