Hi!
Best Practices document [*] about MSA and iSCSI deployment (over 10 Gbps interfaces) suggests that a dedicated "private" network (backend) between MSA nodes and Server hosts should be setup totally separated by the "public" network counterpart (frontend) between Server hosts and Clients.
Setting up the "private" network by using two standalone (not backplane stacked) Aruba 3810M is totally possible especially if two 10Gbps interfaces per Server hosts (of four you have per Server) are going to be used to cross connect to both Aruba 3810M switches.
Probably, given the topology suggested on Best Practices, you lack of SFP+ SR Transceivers (to cover the frontend side) to uplink to a third dedicated switch (or better here to a virtual switch made of two additional ones)...or maybe, if uplinjd are 3 meters long only, you can use other 4 more DACs instead of purchasing more J9150D for frontend.
[*]
https://h20195.www2.hpe.com/v2/getpdf.aspx/A00015961ENW.pdf (page 42)