Unlike VST3 there is not one single standardized place a 32-bit or 64-bit VST2 plugin gets installed too. there is a pre-defined list (see the software's documentation, note at link below)
Most likely you have a search issue in OBS, where even if the plug-in is installed: it may be not installed in one of the folders which OBS searches for plugins. last I check it will not work with 3.x also not all 2.x VST plug-ins work properly with OBS (many I had tried do not).
Well, the OBS software supports VST 2.x plug-ins.
