Brokesome!

As a rule, depending on the $ total amount being requested for withdrawal, your account may/may not be reviewed for the type of activity/trading being used.

If a broker clearly states in the Client Agreement (and/or Terms of Service) that scalping is fully allowed, then you're in the clear.

Otherwise, it's up to a broker to decide whether to honor the withdrawals from scalping activities.
...It doesn't sound "fair", but at least it's not "sugar-coated".