Yes. 1SE runs on iPad—it's the same iPhone app at iPad size, so you get the iPhone layout rather than one designed for the bigger screen.
Use it on one device at a time. Your projects live on the device you're using, so a snippet added on your iPhone won't turn up on your iPad by itself. To move a project across, restore from a 1SE backup on the other device. That needs a Pro subscription, and it replaces what's on the device you restore to rather than merging the two, so it's worth picking one device as your main one.
More on using 1SE on more than one device.