This is simply false, and moreover, false in each of its particulars.

First: as the appeal opinion clearly states, there's still an open case against Ulbricht for the Force-related murder-for-hire scheme in Maryland. The charges have not been dropped.

Second, evidence of the murder-for-hire charges was presented in court. It was an element of the conspiracy charge. Not only was it presented, but it was presented in a way that Ulbricht's defense was obligated to rebut it.

Finally, the murder charges were presented again during sentencing, and proven to a "preponderance of evidence" standard during that process as well.

These details are all spelled out in the appeals decision.

I thought they couldn't even prove that the people to be murdered even existed.

They don't have to. In federal law (and in several states), you're guilty of attempt if prosecutors can prove beyond a reasonable doubt that you had the intent to commit a crime, and took some substantial step towards it.

They've more than cleared that bar here.

Even if there is no actual target?

For example: Is the rational that if I earnestly believed I was planning on murdering someone who I thought existed, that it is the lead up and consideration that is the crime, rather than the actual attempt (which could never happen)?

Yes. That's why we have a crime of "attempt". You do not need to have a likelihood of success; it only needs to be proven that you did intend, and that you took substantial steps. Ulbricht spent more money on these crimes than most people earn in 10 years.