Regarding your question - yes, you will loose access for all machines within this physical host. Of course, it depends which component failed. If it is disk - it is kind of problem, if it motherboard - it is much easier. In general hardware recovery is easier as hypervisor is hardware-agnostic. At this point of time there are a lot of vendor specific technologies you can use to have highly available services.
Resource Pools (vmware) - are NOT able to aggregate multiple physical host resources (cpu,memory,etc) as somebody mentioned above, so if you have 2 physical host (let's say 1CPU quad cores without hyperthreading - 8GBRAM each) it will NOT be possible to have 5vCPU-12Gb VM there. Resource pools are logical ones, they are not able create supercomputing systems. Right now, this is a way of controlling resource utilization.
Availability (vmware) - it is possible to use technologies like High Availability (HA) which allow you to have automated recovery (based on my experience within 1-2min) of all VMs in cluster automatically, IF you are using Storage Array (NAS,iSCSI,FC) and keep all VM files there. More over HA works only in case CPU, RAM, Motherboard failure, it is obvious it will will not work of Storage Array goes down. To prevent RAID/Controllers failures people use Replication, Storage LUNs mirroring etc.
If recovery within 1-2 min is not an option there are technologies like Fault Tolerance (FT) which allow to achieve ZERO downtime of VM in case of failure by keeping shadow(running) copy of configured VM. But this technology also has a lot of restrictions - problem of fault tolerating VMs with multiple vCPUs is not fully solved.
Overall, each solution depends on your goal.