If a party is viable they strictly speaking aren't a spoiler. 3rd party wise in the US. 3rd party candidates in local elections are great. In my state there are plenty of offices Republicans run for uncontested. I would vote sight unseen for any non Republican aligned candidate running against them.

National elections....... 3rd parties running here can't help but be spoilers. First there's 50 separate sub elections they have to qualify for in the first place. Most don't even qualify for half that at best. So they've already lost. Then on the off chance they somehow won one.(never really happened in 250 years) There's the EC system and delegates. Some states are winner take all, some proportional. And while they're supposed to vote to represent the states population. Faithless electors are a thing. Meaning 3rd parties just lost harder.

Its something like a .00000001% chance with an over 6 sigma confidence rating. You have better odds of getting struck by lightning multiple times while dancing the Macarena.