Yes, one of the big differences is that 'tar' lets you break up larger filesystems into smaller, more manageable DLEs, as well as excluding specific files or file patterns.
Be sure that you use 'tar' version 1.13.25 -- nothing older, and nothing newer, until you hear that someone has certified it to be compatible with Amanda. (The latest version, 1.13.92, causes indexing not to work.) Also, I've found that 'tar' seems to take longer in the estimate phase than do 'dump' (and 'vxdump'), but for all I know, that could be due to local influences (e.g., disk traffic). Or has anyone else also found it to be the case that 'tar' estimates take longer than those from 'dump'? -- Mark