Here's the take from somebody who just returned from Big Island. I struggled with exactly the questions you're asking while there.
First of all, there is amazing coastal sceneries and volcano fields in the island you can capture without having to worry about park boundaries. But watch the winds on the coasts, they can suddenly become very strong when you leave the land just a few 10s of meters. At one point in South Point my Mavic wasn't strong enough to fly back and was over the ocean. I thought I was going to loose it and saw it right in front of me, 50 meters or so away. It wasn't coming any closer, even in Sport mode! The way I got it back is by diving below the level of the cliff I was standing on (where the wind was slower) and flying back, then quickly jumping up above the cliff and landing.
Filming lava was on my mind all the time. I'm a big fan of our NP system but personally found the safety boundaries imposed in Volcanoes obnoxious. For instance, you can hardly see the lava in Kilauea even when the lake level is high (within 25 m below the level of the crater) because it's a mile away from Jaggar and the angle is bad -- far away from the caldera boundary, which is still a ways to the lava lake on the other side of it. On the windward side (where Jaggar is) it would still seem much safer than standing on the edge of Grand Canyon, which is perfectly legal. I thought about (and tried) launching just outside the park but the closest point, a golf course north of the crater, is >2 miles away from the lava lake, so I was at 60% battery level when I had only crossed half the caldera. Similarly with the lava ocean entry -- the safety line is so far away so it's hard to see much with bare eyes. Though it's better than the crater where you see almost nothing. Overall I'll say (and this is just my opinion) that Volcano NP's rules BEG for evasion by drone flyers and hikers ok with taking a little bit of calcuated risk (and yes, I've done extensive research on those risks and how to minimize them, and no, I didn't evade any rules myself).
The park boundary at the ocean entry is indeed about 1-1.5 miles away from the site, but VLOS is pretty good and I think it can be done. I'm still beating myself up for not trying but I was too busy encouraging/carrying my tired children. That said I took a decent video with 135mm equivalent focal length lens on a tripod from the boundary enforced by rangers. I'll be excited to hear what you report and watch the winds!
Btw I'm not encouraging this, so this is just for information disclosure purposes, but according to the guys renting the bikes in Kalapana there are no rangers at the entry before 3 pm, so you could launch launch from within the park. Also, I'm also pretty sure you could launch/land closer to Kilauea lava lake from within the boundaries without being caught, say from one of the hiking trails or from near Jaggar. But doing this could lead to tighter rules in the future, and is obviously illegal, so I didn't do it and wouldn't encourage/want others to do it.
