I'm not sure if there is an all-in-one product that covers the HX high level objects down to the detailed equipment health right now (I suspect you will eventually see this from Intersight, as Intersight does a fair amount of monitoring already).
I have seen customers use some Cisco Prime configurations to monitor UCS compute and network level and VMware level objects, which would cover most of the component layers of Hyperflex. See https://www.ciscolive.com/c/dam/r/ciscolive/emea/docs/2016/pdf/BRKDCT-1885.pdf on Prime.
As previous poster mentioned, Cisco Workload Optimization Manager does have monitoring capabilities for HX, https://www.cisco.com/c/dam/en/us/products/se/2018/9/Collateral/optimize-hyperconverged-hyperflex.pdf , although I don't have personal experience with that.
Having both your UCSM and Hyperflex smart call home correctly configured will get you pretty good health status and event alerts for both equipment and cluster health. As for performance at VMware ESXI host and guestVM levels, you will need something like previously mentioned Prime or other products that correctly monitor UCSM, ESXi host, guestVms, network interfaces, HX cluster object health, etc.
https://www.cisco.com/c/en/us/td/docs/unified_computing/ucs/ucs-manager/GUI-User-Guides/System-Monitoring/4-0/b_UCSM_GUI_System_Monitoring_Guide_4-0/b_UCSM_GUI_System_Monitoring_Guide_4-0_chapter_01.html
https://developer.cisco.com/docs/ucs-dev-center-hyperflex/
Most of Cisco's products have REST api interfaces that expose most objects that you would want to monitor, and are usually preferred over traditional SNMP
HX does not currently have a SNMP stack, and I hope they don't create one as SNMP always seems add memory/cpu utilization overhead issues.
If you are trying to go down the opensource/free tool path, then I've seen a few customers string together Cacti, Nagios, Zabbix, etc, but that usually takes a lot of work.
Kirk...
