Can I use my phone for tethering/as a hotspot with a cruise package?

 If your domestic service allows tethering.

If you have purchased a cruise package, be aware it comes with a very limited amount of data. You're not using your domestic plan you're either using the hundred megabytes that came with the 60 dollar plan, or 1 gig that come with $100 plan 

https://www.att.com/international/cruise-packages/

If you're allowing someone to tether It would be sufficient to send an email, or a text message.  Using it for phone calls would use up the modest amount of data that's included and you would incur overage charges after that 

Be very cautious