Is it possible to get the NewsScrollerJP to catch images inserted via JCE-editor as well (and not just mosimage) ?

You should be able to do that but the problem would be this...
You select say,150 characters and a news has inage tag in it like
<img src="http://www.xyz.com/images/blabla.jpg">

this means these characters in these about 50 characters image tag are counted in the 150 character limit. So your actual text would be just 100 characters in this news. In another item without image the text would appear longer with 150 characters.

Second problem, if your image is after some text, say in above example after 130 characters, your image tag would be cut at the remaining characters and you will see something like
<img src="http://www.x...read more...