Qt3 is maintained for historical reasons but builds are expected to be perfomed against TQt3. The current version is 3.5.0, implying, yes, ABI changes.
When built in TQt3, qmake is renamed to tqmake and returns the following:
Qmake version: 1.07a (TQt 3.5.0)
This is with the R14 development branch.
Darrell