Hmm, if you've got your own bullet graphic it used to work well in good old RH X5: Right-click the bullet item > Select Bullets and Numbering > Specify a Bullet image
RH7 (less old, but in my humble opinion also less good than X5) has same fuctionality, but it has stopped working for me:
When using the Bullets and Numbering dialog for inserting an image as a bullet, it initially works fine. In my case the path to the graphic is a relative one (e.g. ../../MyGraphics/MyImage.jpg). But only until I close the topic. The next time I open it, RH has forcefully corverted the path so it points to a non-relative location on the C: drive (where of course the graphic is not located). Consequently I get the dreaded red placeholder square instead of my bullet graphic.
This has effectively made it impossible for me to use own graphics a bullets since I upgraded to RH 7. I wonder if there any reason behind this behaviour?
Yes thats a bug in RoboHelp 7. It shows up when the style sheel is not located at the same level as the topic you are currently editing. Then RH includes a wrong path into the style sheet and the image does not apear. You can manually edit the path and correct it in the same list style dialog though. I have always been using images for dashed list styles if required.
I just saw that the bug is evidently fixed in RH 8 so perhaps you might try a service release: http://www.adobe.com/support/robohelp/downloads.html