If I reveal an Undertitan with the Move Trigger from Rift Herold, will I get the 2 Energy?

Yes. If you reveal Undertitan with Rift Herald's move trigger, you get the 2 Energy.

Here's why: Rift Herald's ability explicitly says "You may reveal a unit from among them" — it uses the word "reveal." Undertitan's "As I'm revealed from your deck, [Add] [2]" only triggers when a game effect instructs you to reveal cards from your deck (per FAQ #10361 and Rule 424.2.a). Rift Herald does exactly that, unlike Hook or Baited Hook which only let you look.

So when you choose Undertitan as the unit to reveal from the top 3, its reveal ability fires, adding 2 Energy to your Rune Pool — then you draw it and recycle the rest.