Yes. I leave ARC 2 on flat always with the bass correction turned on, but that doesn't mean I know what I'm doing Hahaha! There are some great meters out there that are cheap or free that will help with all of this. The T-racks Meter is very handy and free with T-racks Customshop free. Toneboosters has EBULoudness which works great as a reference tool. Klanghelm has VUMT for $10 and Hornet has VUMeter for less than $5 sometimes. There is also Voxengo's Span which many around here use and love. It's free.

I have found that I had better end results Not applying ARC 2 into my Ozone module chain. Works good for the mixing process but I didn't like it in the mastering process.

the need for arc is the same whether you are mixing or mastering.
 
it corrects YOUR ROOM.
 
you should not ignore your room when mastering.
 
that said,
it's easier to think of ARC as being only relevant WHILE MIXING......
and always have it off for everything else.
 
 
i use it to begin mastering, only to check EQ....
if i like my EQ the way it was when i was mixing, 
and my mastering chain (Linear phase EQ, Linear phase Multiband, L2 limiter) does not alter the EQ enough to make any big changes, i then delete ARC from the effects chain and continue with mastering.
 
it WILL screw up your gain staging when mastering. just turn it off after a precursory check.
 

I would have thought that it would be every bit as important to have ARC switched on during mastering as it is to have it on during mixing. Put it this way - if your room is such that ARC makes a huge improvement during mixing, how could it possible not improve the mastering process in the same way? If ARC is correcting a loud resonance at 100Hz then how could bringing that resonance back during mastering be a positive thing?

I always make an ARC 2 bus and place it after the master bus. That way it doesn't effect gain staging or my mastering chain. I have to turn it down to -6 or -9 and I have to remember to turn it off before export or export from the master bus. I can see where it would cause problems with the standalone Ozone. It works great on standalone in T-Racks.

I have been using ARC2 for almost a year but it is until recently I had just discovered a very important feature in the edit page. There are pre and post buttons with a trim knob. You can use these features to adjust so that your volume level is evenly matched before and after processing. You can also toggle between mono and stereo. I have been reading about the importance of mixing in mono. After I had tried mixing with the  mono knob my mixing had improved significantly.

Just so I understand.....with ARC active......trim the ARC output to match the overall output so ARC doesn't boost the output, I think that was part of my problem. ( that makes sense to me) lol

Yes. Kind of the same principle like using a compressor, after the gain reduction you might want to make up the gain so that your output matches the input.