I've noticed whenever egging to go Onos that as soon as I spawn, I have to heal. I'm assuming it's because the HP for a just-hatched Onos is still set to 700 HP rather than the 950 it current has in 3.2b2.

This is actually automatically handled and shouldn't require updating even though the Onos health changed. Basically when you gestate the Percentage of your health stays the same (ignoring the effects of innate regen). So if you have 50% of your health as a skulk when you egg you'll have 50% egg health, and when you emerge as an Onos you'll have 50% of your health there.

I tested this several dozen times in 3.2Beta2 and couldn't reproduce the issue as you described it. If you can get me some reproduction steps please PM me with them, and I will re-open this report.