can connecting a tristate buffer output to 0 or 1 make problem?
The GND symbol represents metal plates buried in the earth. It should always be drawn pointing down. You can't earth something in the sky.
You need to state in your question whether the buffer is enabled when the enable input is 0 or 1.

Is there any problem to connect the output line to 1 or 0?

There is no problem if the output is in tristate because it is floating.
If the output is not in tristate then it should not be connected to a line that is being pulled high or low by another device. If you do then high currents will result and the logic level will be somewhere in between 0 and 1 so it will be undefined. There should only be one device putting data out on the line.

What is your answer about the second circuit which is made with transistor?

There is not enough detail.