Just looking at the top of my head and these words are written :P ....
In Attitude Mode, the IRS will provide:
• Attitude
• Attitude rates
• Heading
• Acceleration
• Vertical velocity
The last one seems to indicate that V/S will be available.
I'm wondering how Autobrakes/Antiskid will be affected (in the various IRU modes). On many aircraft types, certain functions of Antiskid require groundspeed, but I haven't been able to find out how much the Antiskid/Autobrake system will be affected.