[BjoernKW]

Sure. As far as I'm concerned experience is experience no matter where that experience comes from.

One thing to keep in mind though is that part and parcel of solving engineering problems at scale is working and communicating with others. If you've been working on these side projects all by yourself then that experience might not be as valuable as if you had worked on these problems in a team. This certainly is possible with side projects, too of course, like when you have an open source project with several contributors or a side project with several remote developers. It's just that the term 'side project' usually implies a one-man-band doing everything by him- or herself.