Would creating an online flash card deck for GRE study help overcome a weak TOEFL score?
This may not be a direct answer to the question, but I think the fact that the question is asked reflects some basic misunderstanding of TOEFL and GRE.

I want to point out the TOEFL and GRE are two completely different tests designed to assess different aspects of your language skill. TOEFL is a test for people whom English is not the first language, and thus the emphasis of TOEFL is whether the test taker has sufficient mastery of English to survive the day-to-day interaction with other students and professors on a English-speaking campus. GRE, on the other hand, is concerned with your ability to express, analyze, and comprehend at a level demanded in graduate studies. Thus what you have done for GRE probably does little to rescue your low TOEFL score, given that the two tests have fairly different objectives. Moreover, mastering the vocabulary is only the first (albeit necessary) step to ace these exams. Even if you have mastered GRE vocabulary through your contribution, there is still a long way to go before you can use English to express yourself fluently.

As someone who have been studying in the US as an international student, I want to also point out, from my personal experience, that TOEFL is really an easy test. Of course when you first encounter the test as a non-native speaker, the level of English demanded may seem unreasonably high. But don't complain yet, because actually living in an English-speaking environment demands even more. There is really no excuse for a low TOEFL score if you really want to study in the US, no matter how many Anki cards you've made.