Yes. The DMCA covers all forms of digital media, so this includes the video or graphics in your alerts as well. However, at this time, outside of rebroadcasting, we have not yet seen DMCA take-down notices for the visual aspects of alerts. It does not mean it cannot or will not happen, as using this content without proper permissions is still illegal.
Early November 2020, Twitch streamer LadyDevann received a DMCA take-down notice, and a temporary ban from Twitch, for her sub alert’s audio — a remix of Cartoon Network’s Adventure Time “Bacon Pancakes” remixed with Alicia Key’s “New York.” This extremely short audio clip is what resulted in the DMCA take-down notice.
There is no “safe” amount of a song you can play without the chance of repercussions if it is not properly licensed. Just because it is under 30 seconds does not mean it is not liable.