(I assume that the same as goes for iPhones goes for iPads.)
Yes, but with caveats. Any iPad with an internet connection can do any messaging, app and data downloads, iCloud and internet access that a Mac can do including receiving telephone calls as well as sending and receiving of SMS/MMS texts using the phone number and account of the iPhone on the same Apple ID as expected.
The unique feature is when the iPad has cellular capability activated. An iPad with cellular capability activated
has its own SIM card and unique telephone number and account but only the Telephone Company knows what that number is]. The iPad's hidden phone number is aliased to the iPhone's number. The user doesn't really see that separation (except on the monthly bill from the telco) but it is an interesting twist.
NOTE: All Apple watches can send and receive any kind of communication an iPhone can with the exception of Face Time (no camera) through a bluetooth connection to an iPhone. Like the cellular enabled iPad Apple Watches 4 and 5 have their own SIM and hidden phone number and are able to connect directly via their own cellular connection. (If the iPhone is within bluetooth range it will be used to conserve the Apple Watch battery.)
