It would be a helpful alternative option I think. I've suggested in the past that you should also be able to limit voting to specific rank as well (Ie only Senior Members and above can cast a vote (but you could chose the member group yourself)). In certain issues it would be helpful to exclude lower ranks. It would also limit manipulation and abuse from alts.
Is it allowed to any voting system?
Yes. Maybe not general governmental elections but many other voting systems are done so publicly. Anonymous voting has it's place but so does public voting (and they both have positive and negatives).
Transparent polls might stop people from voting against the "gang" don't you think so?
They would be free to create their own anonymous poll.
Public voting systems are generally bad in my opinion. Even if you don't care that people know what you are voting you will likely take into consideration what others might think of you even subconsciously. Which could actually reflect on the voting result negatively.
This is generally the issue, but you can set the poll here to see how the voting is going on without casting a vote which can also influence things. If you were going to vote one way but then see the majority are voting another you either might just not bother or vote for the one that is likely to win anyway since you feel your vote may not count.