Not really. A Dim can usually go up turn 2 in upped decks and turn 3 in unupped ones. I'm sure you know there's no unupped deck that can kill in 3 turns. After that Monoaether autowins. Hard counter.
I actually used two definitions depending on if we're talking about a card or a deck. I very clearly only compare cards when I say PC is a counter to Dims.
Then I very clearly compare decks and how combinations can turn soft counter cards into hard ones. These cards are in theory counters, but need a little help (because Dims are OP *sillyface*).
Right, Heal mitigates damage. Unfortunately it's one-time and the mitigation does not turn it into a soft counter because it's not powerful enough (as I mentioned). That's why Immorush wins most of the time. If anything you're describing how a faster rush is a soft counter to a rush, but I think intention is an important factor here.
When you're facing a rush with another rush, you don't really talk about "counters", because it's more up to the nature of the decks and the draws. For instance, an Aether rush wouldn't call itself countered if it got rushed by Life.
Now, if USEM had CC instead... let's imagine two Fire rushes (non-Immo) where one has 6 Rage Potions and the other has no CC. The CC is a soft counter to the creatures, but by no means a complete counter because you're still just trading one card for another (for a slightly lower cost).
If these rushes were Immorushes, it'd be a counter. RT's would be even harder counter. If it had no PC or Bolts, Dims would be a hard counter. If it had Bolts and no PC, Dims would be a softer counter, but still result in an easy win most of the time.
Man, this is off-topic.