We have a relatively new Dell R440 blade server with 2x32GB SD cards, 2x480GB SSDs, and 8x1.2TiB Hard Drives in a 7.2TiB RAID6.
Not wanting to waste a chunk of the SSD for the ESX-OSData installation, we were thinking of doing the install onto the SD cards, and then using the HD array for the ESX-OSData portion, leaving the SSDs entirely for VMDK usage.
Does this make sense?
If you are going to prepare your hosts to work standalone, or without shared storage or with vSAN, then only SSD part will be utilized.
Please review your environment requirement carefully.
Since your host has disks, I'd suggest that you get rid of the SD cards, and configure the system to boot from the HDD RAID set, so that ESXi gets completely installed on the disks. That way you can use the complete SSDs (assuming a RAID1) as a VMFS datastore.