as far as I am aware you can use any desktop manager shortcut in WebDesk.
However linking directly to a file could be a security issue and will most problably be blocked by the browser.
You could try to place a label on a window and insert a A HREF link to a UNC Path that brings the user directly to a intranet folder where the excel is located.
However I have not found a way to remove the other LANDesk Desktop Manager options from the actions menu in WebDesk. Maybe you know a small trick how to get them out of there
If you mean the generic desktop management connector then this is not implemented at all in WebAccess. DTM is only implemented for LDMS currently, so no generic, SCCM nor ZENworks.
On your second question, you can add a shortcut into a WebAccess shortcut which launches a URL. I've used to launch all sorts of stuff in the past. You can also add a webpage into WebAcecss dashboards too.