Using Aerospike without SSD
Not at all! Aerospike is a great in-memory key-value store, typically as fast as Redis, but that also scales super easy.

You can check the different configurations possible on Aerospike here. So if you can fit all your data in memory, Aerospike will work as well or better then any other in-memory database. The SSD optimization is useful for larger data sets that would be too expensive to fully store in memory and Aerospike is also optimized for that use case.