Hi,
The marquee mode has not been brought to the Perspective Alarm Status Table as of yet. There is a post on our ideas and features board asking to implement this feature here: Perspective Alarm Marquee/banner | Voters | Inductive Automation. Adding your vote to this idea will give it more priority when our developers go to take a look at what the community is asking for when planning future updates.
As for rolling your own solution, there is almost certainly a way to get something working if you're comfortable with CSS. While not directly related to the Alarm Status Table, there are some other forum posts regarding creating a marquee board type solution that you could use as a starting point Perspective Marquee Table - #2 by Cody_Daniel.