Just googled HTAG "
"H-JTAG is an ARM debugging and programming toolkit "
And for Keil I did not need to google because I know that tool rather well.
There are MANY different programmers for ARM. AVR or AVR32 are NOT ARM based. That means, you can not use ULinkx or HJTAG for the AVR. Going with AVR means for most users going with the Atmel software. Whether that is a benefit or a problem that is up to your judgment.
It's probably not the answer you were hoping for but I hope the facts help you nevertheless.
Bob