Hi Paso,
I guess your question relates to the difference between what is "required" verses what is "recommended"? It is possible to configure ISCSI in Windows natively without installing DSM or host utilities for connecting to NetApp Storage however installation of the host utilities is considered best practise to ensure optimal configuration for failover and performance.
https://www.netapp.com/us/media/tr-4080.pdf (Note: Point 15 in the summary of best practises on page 38)
I hope this technical report is useful for providing recommended best practise.
/Matt
If this post resolved your issue, help others by selecting ACCEPT AS SOLUTION or adding a KUDO.