vSphere 5.0 or later can identify and tag SSD devices and use them as Host Cache. According to vSphere Resource Management guide, Host Cache will be used as Write Back Cache when VM memory needs to use vswp file. So if I understand this correctly Host Cache will help when VM needs to swap OUT to vswp file but when VM needs to read swapped page (swap IN) it still needs to read from vswp file.
You can use PSA SATP claim rules to tag SSD devices that are not detected automatically.
Only devices that are consumed by the PSA Native Multipathing (NMP) plugin can be tagged.
In my demonstration I have VMFS-02 that is identified as Non-SSD. Well this is not SSD based LUN so it is correctly detected, but using SSD tagging feature I can fool ESXi to believe this LUN as SSD.