Not exactly a scientifically-controlled test, but I can confirm that sharing over pure AppleTalk DDP works on Netatalk 2.0.3, at least under Ubuntu 8.04 Hardy Heron.
My test client is a PowerBook 1400, Mac OS 8.1, AppleShare Client 3.7.4 on top of OpenTransport 1.3.1.
I'll next test against 7.6 and 7.1, and after that start upgrading Netatalk on Ubuntu until I can get it to fail.
At a certain point we may start running into volume size limitations in earlier versions of Mac OS, but there is an option to artificially constrict reported volume size in Netatalk. (Interestingly, this feature was dumbed down in the most recent release of Netatalk to only function with Time Machine Backup volumes, not normal AppleShare volumes. The reasoning was that the code to check the size of all files on disk was too inefficient unless it had access to some special TM features. But on very small volumes, like the ones we might use in vintage computing, it's hard to believe this would be an issue.)