E-RTMP and IVS support

Amazon IVS Real-Time Streaming does support E-RTMP (Enhanced Real-Time Messaging Protocol), but there is no indication in the available information that E-RTMP supports H.265/HEVC encoding for single-track video.

According to the documentation, IVS Real-Time Streaming supports video with the H.264 codec using the Baseline profile. The service supports both standard RTMP/RTMPS and the enhanced version (E-RTMP) which enables multitrack video capabilities, allowing you to send multiple video qualities to your IVS stages for adaptive bitrate streaming.

The E-RTMP multitrack video feature specifically enables publishers to send multiple video qualities in a single RTMP stream to IVS stages, which then delivers these different video qualities to subscribers as simulcast layers. This allows viewers to watch in the best quality for their network connection.

For testing E-RTMP multitrack video, you can use OBS Studio which supports this capability. The documentation mentions that once you've created a stage using the IVS service, you can configure OBS Studio to publish multiple video tracks to your IVS stage using the E-RTMP protocol.

However, there is no specific mention of H.265/HEVC support in the context of E-RTMP for IVS Real-Time Streaming in the available information.
Sources
Amazon IVS Real-Time Streaming now supports E-RTMP multitrack video ingest - AWS
IVS RTMP Publishing | Real-Time Streaming - Amazon IVS
IVS Stream Ingest | Real-Time Streaming - Amazon IVS
Amazon IVS Multitrack Video: Broadcast Software Integration Guide - Amazon IVS

No, it's currently H264 only.