Will Apple keep my data on iPad when I send for glass replacement?

No, you must backup your data before sending in your iPad for repair.

I doubt you'll get the same device sent back to you. Most likely they'll replace the whole device and they won't bother transferring the data. It's not their responsibility.

As has been stated, but I feel needs reinforcement,

You'll need to backup you iPad's data.

Either through iTunes on a computer, to a "cloud", offsite server storage, like iCloud or Dropbox, or to a external storage device, like special external portable WiFi hard drives made for iDevices from Seagate or Western digital OR special USB flash drives made for iDevices like those from SanDisk.

If you have important data on your iPad you want to keep, you need to get that data backed up to another source location.

Good Luck!

Backup is always a good thing. I suggest that you backup both to iTunes and iCloud just to be sure.