Undetected Matchmaking?

It is possible I can play in matchmaking servers without taking any ban?
And what security do I have if I buy and take ban in my steam?

You can only getting banned from overwatch this depend fully on your playstyle and your settings.
A driver (ring0) will keep you undetected.
At the moment its only available for 32bit system. You can play on 64bit also but without driver. The 64bit driver is currently in alpha testing phase which means it will be released soon.
Well and aimware will not take any responsibilities if your steam account get banned since cheating is always a risk.

But playing with 64 bit is also safe than 32 bit?

[quote='TOYmakeR' pid='35364' dateline='1418361108']
But playing with 64 bit is also safe than 32 bit?
[/quote]

Yes, the only reason it wasn't safe before was the driver being available for 32 bit only.
As of 12/11/2014, there is driver support for both 32 and 64 bit.