Yes, you will need to use custom CSS and the image property for lists.
You can find the syntax on CSS reference site, the property will be
{list-style-image:url(imageURL);}
in front you will need a selector to target lists in the area of your choice, and put the rule in Main Options > Fonts & Custom > Custom CSS Rule box.
A general rule for ALL list would be
ul, ol {list-style-image:url(imageURL);}
One just for widgets would be
.widget ul, .widget ol {list-style-image:url(imageURL);}