Product support for access gateway indicates that JRE is not needed for SPS Access Gateway but there is a \JRE folder in the following Path reference
<secure-proxy install path>\install_config_info
SPS Access Gateway: 12.8.8
OS: ALL
AG uses only JDK, and not JRE. The JRE folder referenced in the 'install_config_info' folder is used by 'install anywhere' during installation and uninstallation only and can be renamed or removed Post installation if flagged for any vulnerabilities (suggestion is to rename or move it to a different location as it will be needed if uninstall is required at any furture date)