a slightly different in details but in principle much much the same here.
download ds3615 synoboot.img 1.03b using existing synoboot.vmdk from other posts.
upload these 2 files into the datastore in ESXi 6.5 datastore where the new Xpenology vm will be created
create a new vm using OS as Other, FreeBSD 64 Bit (this gives the choice of VMnet3 in nic later)
remove the harddisk that get automatically put in by the template
add a harddisk, SATA controller 0 slot 0 using synoboot.vmdk (which points to synoboot.img by reference), either dependent or persisent doesn't seem to make a difference
add SCSI harddisks for NAS data
nic get its mac address from synoboot.img so if you need to change the licence or mac, then editing this img file has to be done
set the nic to vmnet3
complete and power up
using synology assistant to discover the vm
connect and when prompt to install DSM, choose auto install from internet and 6.2 (without update x) will be installed
after reboot etc etc, 6.2 update x can be installed.
note: could not get the various 6.1 pat files to work, downloading directly from the internet worked a treat. success with both HP N36L and N54L
can post screenshots if others are interested