They are in the simulator but they are not exposed to plugins.
Forgive my lack of knowledge in this area, but could someone write a plugin that calls them if they knew the channel name. Or are they just not available at all?
PiBoSo defines what is sent to the plugins. If he thinks slip angles are useful, he can easily pass them in the plugin interface.
Notice however that PiBoSo philosophy for data passed to plugins seems tobe "GPB only passes telemetry data", i.e. data accessible on a real bike via telemetry.
Slip angles, for example, may not fall in this category (like many other internal state data) so I doubt he'll do it.
What would you use them for anyway ?