Mac OS X Server 10.2/3/4 can all be configured as NetBoot hosts. Newer versions of OS X Server are, in my experience, easier to manage and run on newer machines which are both faster, usually have better storage/networking, and sometimes cheaper.
NetBoot, on Macs, and what these versions of the OS can support, is only for NewWorld Macs, and so can only boot the iMac/233 and newer. If that's what you're thinking of, I wrote a
super brief primer on NetBoot here.
If I'm remembering right -- some network booting code has been found in various things pre-newWorld but it was never productized and as far as I know nobody's gotten it running, yet. When/if they do get that running, stock OS X Server (and in fact OS X server at all) likely won't be able to run whatever gets built.
You don't need Mac OS X
Server for just file sharing, however. I'm tempted to say I'd recommend against OS X Server for
just file services, as well, because "Easy Mode" wasn't really added until OS X Server 10.5, so you're jumping into a product Apple was aiming higher than where ASIP had been before. (It's fine, but there is a learning curve that's steeper than for plain file sharing in the client version of the OS, so, for whatever that's worth.)
To add to the comments about using 10.2 as a bridge machine: 10.3 should also be able to file share to AppleTalk-only Macs (Regardless of whether the AppleTalk is on LocalTalk or Ethernet wiring) and 10.4 can share AppleShare IP (so as far back as 7.5.x and newer w/ OpenTransport and AppleShare updates, possibly 7.1 if you extract the 7.5.x OT+AS updates by hand, and as new as macos 11, that I've tested.)
The main logistical advantages of newer versions of the OS are, again, newer hardware, faster storage, and
bigger volumes, 16TB for 10.3/4/5, bigger for 10.6+. If most of your collection can run 7.5+ then standardizing on 10.4 for most things
also has the benefit of running on cheap early Intel Mac minis and in virtual machines.
(The QS and QS'02 can run 10.2/3/4 and arguably 5 very well, my points about logistics are more for anybody else considering running a Mac OS X Server machine as a bridge. I should probably get some of the media and look into writing up guides on how to do a couple things with a few different server OSes, including shoring up my unfinished guide on ASIP6.)
All that said: You can use Netatalk 2 to host files for vintage Macs as well, so using a slightly newer vintage Mac to do it is a style choice, basically.