I don't understand what you're asking. When you say "on forex", do you mean "in the interbank market rather than through a spreadbetting company?". If you do, the answer's yes.
But don't imagine that anything/anyone other than a spreadbetting company is "the interbank market". That isn't so at all. Most retail forex brokers are themselves market-makers, and they hold the other side of your position just like a spreadbetting company can.
I suspect that you're assuming that the relevant distinction here is between "spreadbetting firms" and "others", but it isn't: it's between "people who hold the other side of your position" and "people who don't". To express that another way, most retail "forex brokers" aren't really "brokers" at all: they're market-makers pretending to be brokers.
Nobody will mind you scalping the market, but (if you're any good at it, which very few people are) nobody will want you scalping them. Most retail forex brokers welcome scalpers, because most scalpers lose, and that's good for the brokers if they're trading against their own clients. But when you start to win regularly, one way or another it will be "Goodnight, Charlie" and you'll need to use somewhere like Interactive Brokers, who really are brokers and don't hold the other side of your positions so that it isn't their money you're winning.