Can I run apps with similar function? Recently I have installed Juice Defender and Greenify.

Unknowingly I ran both of them. The result is pretty great (battery almost stopped discharging). Battery levels stood constant for hours when my screen is off.

Is it good to run both of these apps together?
Typically it is advised not to run two apps that have overlapping management areas.

If you aren't seeing excessive activity/drain due to the two apps stepping on each others toes then it is not bad. From your take so far, it does in fact seem good in this case.

You wouldn't, for example, want two anti virus software running side by side in the same environment. That would usually be bad.