For DietPi in general NO (for now).
All Odroid devices will stay on Jessie for the moment ( yet )
Why? Please seach forum or read on github.
For DietPi RPi builds YES and NO.
DietPi RPi Stretch build start about one ago. RPi Stretch status
But most people don’t notice, read, or follow this up.
Where are some “special” RPi builds, e.g. for AMIBerry or Allo, who take a little bit more time, to get it up and running with Debian Stretch as base.
You can get or download DietPi for RPi Wheezy | Support Ended (22nd June 2016) as well.
Sure, no DietPi updates, no fixes, no support by us any more, but it will work until now.
And it has Debian 7 “Wheezy” LTS until 31st May 2018 for security fixes by Debian.
Then we will take the link down.
To get it clear: