a couple things about sitemap
Using Jamroom
Actually, the seamless module does have an index.tpl template which expects the modules to list as an 'options' post, so your error that there isn't an index.tpl template is wrong.
Also, on my test site mydomain.com/timeline does list all timeline items.
What versions of the seamless and timeline modules are you running? Make sure they are up to date, or reload them if they are.
hth