Yes. During registration, you can select both the 5K skate and the 5K run/walk events.  You will be charged the registration fee for each event and you will receive two separate race bibs, one to wear for the skate and the other for the run.
However, if you just want to stroll around and enjoy the music after your skate event, no need to also register for the run/walk, although registering for it will give you the best views of the bands since the inner lane of the streets is designated for race registrants.
If you want accurate chip timing for both events, register for both and plan to complete the skate before the start of the run/walk so you can start at the designated start time for your wave (see next FAQ question for wave start times).
The 5K run/walk starts 15 minutes after the start of the skate. If you can finish the 5K skate in 15 minutes, you should have enough time to switch to your running shoes and race bib for the run, then line up for the run/walk. If you finish the skate after the runners have started, let us know and we can adjust your timing results accordingly. Go for it!