Code for the visitor generator is old and does not use the tracking API, instead it rebuilds tracking requests manually.
Instead, Visitor Generator should take a "Piwik access logs" (requests to piwik.php) from demo.piwik.org by default (but possible to put your own custom access logs) and it should replay this log file, for N days and playing it M times per day.
the other advantage is that this will be usable for API consumers who wish to "initiate" piwik DB with a fixed set of data and run their own tests on it (rather than the current "random" data sets).
Also, logs will be more "standard" and not use the many random strings etc.
(In ) Fixes #2458 - Visitor Generator now based on a "piwik access log, combined format" that is replayed faking Time/IP/User Agent/Accept language header. The file can be swapped for any other log file containing requests to piwik.php
The current log file generates a little bit of ecommerce activity, as well as various pages & custom variables (based off Forum.piwik.org log file)