Yes. They were charmable.
Dire charm was simply a -1000 mod charm. The mobs that were flagged as charm immune were not able to be dire charmed either. This means that the NPC was not specifically flagged as charm-immune. The fact that magic stuff lands on them also means that they are also not flagged as magic immune.
Combining these 2 observations
1) the hatchlings were not specifically flagged non-charm (evidenced by dire charm).
2) the hatchlings were not resistant to MR (evidenced by the ability to root/slow/etc).
Logically yields that the hatchlings were charmable via normal means even if it was not something commonly done prior to SoL.
I spoke with Alunova about this on Saturday.
Edit:
http://www.therunes.net/forums/viewtopic.php?f=3&t=936
Is the thread I was trying to dig up. Talks about using DC on hatchlings and CoD (PoP charm) in ToV. There were mobs that it landed on while others were specifically flagged as immune. So, even HoT Wurms were charmable when enchanters got a higher level-cap Charm.