I've done two different types of integration with Salesforce. If they are using Pardot then they can expose a simple form end point that you can POST to. I made an Ajax form and then in the surface controller I just do a post to the Pardot Form endpoint. Works well and hides the stupidly open form for collecting the lead / contact. We also have a few API endpoints - these are harder to do as you need to do oAuth - get a token etc. and on the SF side build an APEX Soap API endpoint (or there are other options) but it's all doable. For forms -> SF I'd probably just write a custom Umbraco Forms action and rePOST to the Pardot endpoint?? As with everything with SF I suspect Pardot is quite an expensive addon though