It's impossible to skip any level/boss/cutscene in the game, because that would make you unable to continue in the game. I'll give you an example:
We call all the levels, bosses, cutscenes and obligatory upgrades as triggers. As Sonic, if you complete Emerald Coast, Egg Hornet, Windy Valley and do early Speed Highway, the game won't let you watch "Amy being caught by Zero" cutscene, because there are many missing triggers (Light Speed Shoes, Casinopolis, Ice Cap, Chaos 4, Sky Chase act 1 and Twinkle Park).
Just like that example, Hedgehog Hammer skip as Amy wouldn't be useful in a run.
About Ice Stone skip, it IS possible to skip the Ice Stone as Sonic, it just wasn't found when I did my TAS. You can get out of there with a spindash jump towards the ceiling from the pool thing in Ice Cap area. It should save around 10-15 seconds.
And I'd like to share you guys a recent found by cjbqulix, that we are working on to find a way to make it save time in a run. It's about a wrong warp using cutscenes:
http://www.twitch.tv/cjbqulix/c/4544111
Basically, if you do things in the wrong order and do a game over before the cutscene after the wrong order levels, the cutscene will be wrongly played. In that video, not many weird things happened, it was just a weird cutscene with a death, but things like appearing in the lost jungle with the Ice Stone can happen! So we're doing a lot of researches in this :)
