Is it possible to mount SharePoint as a volume in 10.6?
System-managed WebDAV connections to SharePoint

Yes, connections are possible. For a volume mounted in this way, the file system type is: 


webdav


I use Finder — in Snow Leopard and in two other versions of the system — with SharePoint. 

To connect

In the Connect to Server window of Finder, use the same URL as you would use in Microsoft Document Connection. 

An underlying problem with the Microsoft service

Information about the characters that you cannot use in sites, folders, and files in SharePoint


  … cannot start a file name with the period character. …


Apps with compatibility issues

A shortlist:


Microsoft Office Excel, PowerPoint and Word 2011 (Service Pack 2) — all attempts to save will fail, expect to see error messages that are misleading
Apple Finder — some attempts to copy or move to SharePoint may fail.


My answer to Ask Different question Why are dot underscore ._ files created, and how can I avoid them? notes: 


requirements of Microsoft Office 2011, when used with a file system such as webdav, are not met by SharePoint. 


When SharePoint does not recognise that a user of PowerPoint or Word with webdav has opened a file, there's risk of dataloss — two or more users overwriting each other's work, with no warning before or after the loss. I can't reproduce this problem when NeoOffice is used to open such files. 

Excel with webdav seems to always open .xlsx spreadsheets read-only. I can't reproduce this problem when NeoOffice is used to open such files.  

(Side note: without file system type webdav, Microsoft Document Connection 14.2.0 (120402) causes dataloss without warning, of extended attributes such as Spotlight comments.) 

More about Finder

With webdav, for files and folders that are already on the SharePoint server: 


Finder seems to be a first class app for renaming, moving or removing items. 


Apps that are more compatible

Another shortlist: 


where Microsoft Office applications fail, NeoOffice and LibreOffice succeed. 


Input/output errors affecting files saved in Microsoft formats

If an attempt to open an Office Open XML file (.docx, .pptx, .xlsx etc.) fails with an input/output error: 


use Microsoft Document Connection to initiate an edit
save a trivial change to the file, close the window of the app that you used for edition
if necessary, quit the app that you used for edition.


Those two or three steps seem to resolve, or work around, the error. 

(If I discover the exact cause of those types of input/output error, I'll either add to this answer or link to a question elsewhere. Early indications are that they occur only after a Microsoft Office app has failed to save with webdav.)