While it is usually good to check release notes the link you provided is to a relatively old release. There are more recent releases which support the 2500 routers. I find release notes for the 2500 at least up through 12.2T. And there are releases of IOS for 2500 in 12.3 (though I do not find release notes specifically for 2500 in 12.3)
The other approach to answering this question is to use the Feature Navigator on CCO, which I have done. I had assumed at the beginning that the 2500 is old enough equipment and OSPFv3 a new enough feature that it was probably not supported on 2500. And while it did not specifically identify OSPFv3 support, I did find the Feature Navigator indicates that image c2500-is-l.12.3-19.bin does have support for OSPF and does have support for IPv6. Since OSPFv3 is the implementation of OSPF for IPv6 I am assuming that this image does support OSPFv3.
We are pleased to announce availability of Beta software for 16.6.3. 16.6.3 will be the second rebuild on the 16.6 release train targeted towards Catalyst 9500/9400/9300/3850/3650 switching platforms. We are looking for early feedback from custome...