If I am understanding your question correctly, I would say yes. But I would personally be careful with this just because this can lead you to use background knowledge which is not going to help you in anyway. With the tiger example and the original premise leading to the conclusion, we can act on the basis of this conclusion being true because of the evidence that is given. Is it a complete 100% bullet proof argument? No. The last lesson about the spectrum on strong and weak arguments can help a lot. The point about making assumptions is to determine if it causes doubt to the conclusion (weakens) or gives support to the conclusion (stronger). It's like going to court and having a piece of evidence presented. Regardless if your client is guilty or not, does the evidence weaken your argument for them or strengthen? Hope this helps!

Like mentioned in the video, outside knowledge is not useful on the LSAT. The goal for us taking the test is not to read an argument and to determine if the argument is true or not, instead our goal is to see if it is supported. For example, if there is an argument of: "On my walk today, I only saw blue flowers. Therefore all flowers are blue." Now, we know this argument is not true because roses exist, however that does not make this not be an argument. Like I said before, we're not trying to figure out if the argument is true, we are trying to break apart the argument into conclusion and premise. Which for this example, the conclusion is "all flowers are blue," and the premise is "on my walk today, all the flowers were blue."