Just found all these little bugs crowding on two of my Pacific Blue Ice rosettes. Any idea what they are? Are they harmful to the plants?

Do they fly? If so, I'd think it's white flies. They sure love that plant!

There are two insects, green aphids and white flies apparently. Eliminate them, not much to think about, they feed on the parts that are freshly developing on plants, soon the entire plant will be covered with a layer of them and then get to colonize other plants.

Macrocentra,
Paleo's right, they are harmful to your plant. A simple solution of dish soap and water can be applied with a spray bottle, doesn't hurt the plant, kills the aphids. Sometimes you have to reapply a couple times, if you miss a spot or the ants bring new aphids to the party. That plant is doing something strange, any time a plant is week it's like ringing the aphid dinner bell. Tough to say if your plant is just chicking in an odd way or is possibly trying to send out multiple oddball blooms, either way, making sure it gets as much light as possible will also toughen up the skin and make it less appealing to the bugs, this could also encourage healthy growth.
'Pacific Blue Ice' is a favorite of mine, goodluck nursing it back to health.
-Sol

Oh no! I have a bottle of insecticidal soap. Would that be okay for Semps? Never tried it on them before.

It has a weird growth pattern going on. That's the central rosette, and there's a bunch of big rosettes growing around it. Now it has those little ones growing in the middle of it. The other two species in the container with it didn't do that.

Just gave every plant in the container a thorough bug bath. Going to let it sit for a while, wash the dead bugs away, and give them another spray.
I'll keep a close eye on them for the next while. There's two other Semp containers nearby. While they look bug free, I gave them a precautionary spray as well.

Thanks for the help.

Sounds like you've got it under control Macrocentra!