The kind of rebootloop you are getting at is the one causing hildon-desktop to crash. In RnD mode disable watchdog and you are able to boot even With crashing hildon-desktop.

What is this list actually? To me these .desktop files are in /usr/share/applications/hildon-home because they Are recognized as widgets.
The normal .desktop resides in /usr/share/applications/hildon
These are the actual shortcuts found in the menu. I believe there isn't such a list as safe widgets, atleast not at the path you just said.

.desktop files are files that links the ui buttons to the real paths