Yes, you can combine subscription and burst billing on the same account, and even on the same server.
For example, if you have a server that only runs for 30 hours per month, you could subscribe for the disk space it uses (since storage is needed whether the server is on or off) and pay hourly burst rates for the CPU and memory (since those are only consumed while the server is running).
This hybrid approach lets you optimize costs by matching the billing model to how you actually use each resource type.