Just tested this with the latest 8.0U1 image and using Rufus x86 v3.22.2009 (Portable).
It reports this:
Scanning image...
ISO analysis:
Image is an ISO9660 image
Will use '/isolinux.cfg' for Syslinux
Detected Syslinux version: 3.86 (from '/isolinux.bin')
Disk image analysis:
Image does not have a Boot Marker
ISO label: 'ESXI-8.0U1-21495797-STANDARD'
Size: 599.7 MB (Projected)
Uses: Syslinux/Isolinux v3.86
With an old menu.c32
Uses: EFI
When pressing "START" to start writing the image to USB it does notice the menu.c32 being out of date and recommends replacing it with an updated one. The fact that it detects the ISOLINUX/SYSLINUX bootloader does confirm that it is bootable.
Post-write the log also indicated to me that this is the fact:
Found USB 2.0 device 'USB2.0 DISK USB Device' (1234:FFFF)
Using 'autorun.inf' label for drive 'ESXI-8.0U1-21495797-STANDARD'
1 device found
Disk type: Removable, Disk size: 8 GB, Sector size: 512 bytes
Cylinders: 979, Tracks per cylinder: 255, Sectors per track: 63
Partition type: MBR, NB Partitions: 1
Disk ID: 0x2572D908
Drive has a Syslinux Master Boot Record
Partition 1:
Type: FAT32 LBA (0x0c)
Detected File System: FAT32
Size: 7.5 GB (8052015104 bytes)
Start Sector: 2048, Boot: Yes
Also performed a boot test in VMware Workstation 17 and both the ISO and the USB Stick I created were bootable.