Are conversations with recruitment agencies confidential?

I was recently hired through a third-party recruitment agency, and the recruiter who placed me in my current position has been checking in on me occasionally. She’s suggested we meet up sometime soon, and I’m curious whether the information I share with recruiters remains confidential and won’t be disclosed to my employer or anyone at my company.

I’ve just discovered that my salary is significantly lower than that of my colleagues, which was quite disappointing, especially since I often feel overwhelmed by my workload. I’m wondering if it’s acceptable to discuss matters like this with the recruiter.