Can't confirm if its nationwide myself but posts on geekzone suggest it is. You should be able to see the Data added on the Skinny app unsure about Spark.
Huge shoutout to them for looking after kiwis like this when contacting family is important.
https://www.spark.co.nz/help/internet/manage/get-support-dur…
https://www.skinny.co.nz/
Prepaid Mobile customers: We've loaded 100GB of data for prepaid mobile customers. This will be available to use until 11pm, Sunday 26 February. This data can also be shared with other devices through hot spotting. Prepaid mobile customers also have unlimited calling and text. This will support those of you who are in areas where data is not yet up and running and those who do not have unlimited or large voice / SMS calling packs.
Pay Monthly Mobile customers: Customers on our “endless” plans have had reduced speed thresholds lifted, so they can access unlimited max speeds. Customers with rollover plans have had data caps lifted, so they can also have access to unlimited max speed data. This will also be available for customers until 11pm, Sunday 26 February. To ensure our network can provide a good experience for everyone our fair usage policy applies.*
Spark rep on FB to someone asking about Data:
"Afternoon Leanne, you won't see the 100GB in your app, but you will see that your mobile data won't decrease until the 100GB has been used. ^Richard"
Can't confirm that myself as not a customer