Eloipool modified for scrypt isn't that difficult and it has vardiff and stratum. Likewise, it's also not hard to modify pushpool to support stratum and vardiff. To my knowledge, there is no out of the box, open source on github pushpool with vardiff and stratum. The pool operators either modified it and didn't release it or use a different poolserver.
I have only granted AGPL licensing for Eloipool, so if someone is running a poolserver based on it without exposing the source code, they are infringing.
Feel free to let me know who, if anyone, is doing this, and I will have a chat with them (and throw the book if necessary).
But first, be sure they're actually infringing: grab a HTTP header from the poolserver and check out the path in the X-Source-Code header.