The client has Crestron thermostats that are controlled from the app on his iPad. If I need to replace the iPad will I be able to setup the app without having the crestron software?

Sent you a PM but figured I would respond for others to see.

Providing the interface is being pulled from the processor and wasn't locally sent to the iPad, Yes. If the interface was locally sent to the iPad than you will need to talk to the original installer.

To check this go into settings on the original iPad and find the Crestron App and turn off "auto-reconnect"
From there open the app, select the Pencil icon at the bottom then select the connection
This will take you to a new screen and just under the Friendly name is "Use Local Project" If this is Off you are all set and just match the settings from this screen to the app on the new iPad. If On you will need to talk to the original installer to either obtain the interface files or have them load the file to the new iPad (You will require the Crestron software to load the file to the iPad).