They might have something to say but it's a fact that they can't make decisions about and deploy many levers of policy independently of the other members of the currency union.
"Independence" is a relative term that defines a relationship between two or more states in respect of an area of government responsibility.
For example, It is possible to have independent criminal law and common monetary policy, like the eurozone or to a lesser extent the uk.
Having a common monetary policy necessarily restricts the effectiveness of fiscal policy. Scotland in a currency union with England couldn't devalue or inflate debt away without the consent and connivance of England. They would be dependent on them.
Scotland would also be dependent on other polities in respect of other areas of policy, for example nato members for defence and eu members for border control.
The notion of absolute independence is for dribbling simpletons like Farage or Gove.
My understanding is the Scottish Government policy is to seek fiscal independence from the Uk. To do that they need monetary independence too.