I know Salesforce has an API which you can use from FMP to access data in read/write modes. Don’t know about ACT but I would expect they also have an API for that purpose.
Application Programming Interface (API) - Describes the process and command structure for interfacing with a specific application.
Salesforce uses the REST technology.
we've implemented FM <> SF integration using Dell BOOMI.
That's the only one ETL that worked with FM out of the box.
It's been in production for about a year now and it's working fine.
We're doing a lot of FM <> SalesForce integration: www.soliantconsulting.com