No need to send a note that you still need your 457 as a decision MUST be made to this application, either to grant or to refuse, unless it has been withdrawn.
Make sure to disclose that you have a 457 visa application on foot, so the 457 visa will not be wiped out by your visitor visa. It happens from time to time.
I remember many many years ago, a US citizen, decided to travel to Australia on an ETA visa, after sometime of waiting for his other visa, only to found out after he rang his migration agent upon arrival, his visa was granted a day before his departure from US. Unfortunately he would need to relodge his application again for other visa again.
Regulation has been amended since, so ETA visa will not come into effect if the visa holder already holds another substantive visa, but visitor visa will.
Not all visa applications made by human, the DIBP computer system has delegate power to grant visas.
The decision on visitor visa may be vacated, if you disclose, when apply for visitor visa, that you have an application is still under processing, then the decision must be vacated.