Yesterday I got a reminded by someone that LEGO Rock Raiders was supposedly shown off at E3, so I poked around some E3 1999 videos and by pure chance the first or second video I clicked greeted me with this:
Yep, that's someone donning the infamous "Chief costume" that you could win a Halloween party of:
In the background you can see booths for Lego Racers, that we know were produced by Freudzon design:
Full archive pages of Lego E3 material from Freudzon Design here:
https://web.archive.org/web/20030315081237/http://www.freudzon.com/lego/kiosk.htm
https://web.archive.org/web/20060901072746/http://3dpreview.com/exhibits.php?picture=lego_e3&num=1
And this very brief shot shows some kind of Rock Raiders display:
Here is a timestamp link to the 20 seconds of footage that we got so you can see for yourself:
There was also an article related to Lego at this E3:
https://www.ign.com/articles/1999/05/12/lego-medias-e3-lineup
Apparently you could win the PS1/N64 controller statues you see in the video, and the 4 games that were shown off were: Lego Rock Raiders, LEGOLAND, Lego Friends and Lego Racers.
New footage of E3 1999 is being uploaded and re-uploaded all the time so more might appear, but I haven't found anything from scouring the rest of the videos I saw on YouTube!