Can I detect hidden or co-eluting peaks (using GC-MS) using OpenLab CDS only without addition DRS software?

Certainly, there are some games you can play that require no software to detect hidden and coeluting peaks. For example, you can detect coeluting peaks by producing a sim of each ion in the ms spectra (as shown by a library) then comparing those to the TIC. In simple cases, there will be a clear difference in shape/area. However, this is a lot of work in less simple cases. For hidden peaks (I assume you mean compounds that are unseen by the detector), you can change the detector or conditions of your method and compare. Are there more or less peaks? What structures does the ms give you for those peaks? If there are more or different structures, obviously there were some hidden peaks in the original method. Additionally, in ms if a compound isn't detected, it can often dampen the signal for other compounds at the same time (since only so many molecules make it into the ms and statistically some of them are the ones that aren't detected). Some compounds dampen response more than others. For these, you can easily detect them indirectly with methods that have a high amount of detectable compounds forming the baseline, though with ms the more junk you put in, the shorter the lifespan of your detector so I wouldn't recommend it (much better with detectors that aren't affected by amount of detection such as DAD).

Anyway, the technical answer is "yes". The practical answer is that software is a tool that makes your life easier. If you have the time and manpower to do the work without the tools, feel free to. You can even do exactly what the software does by hand if you want. I'll leave that decision up to you.

Certainly, there are some games you can play that require no software to detect hidden and coeluting peaks. For example, you can detect coeluting peaks by producing a sim of each ion in the ms spectra (as shown by a library) then comparing those to the TIC. In simple cases, there will be a clear difference in shape/area. However, this is a lot of work in less simple cases. For hidden peaks (I assume you mean compounds that are unseen by the detector), you can change the detector or conditions of your method and compare. Are there more or less peaks? What structures does the ms give you for those peaks? If there are more or different structures, obviously there were some hidden peaks in the original method. Additionally, in ms if a compound isn't detected, it can often dampen the signal for other compounds at the same time (since only so many molecules make it into the ms and statistically some of them are the ones that aren't detected). Some compounds dampen response more than others. For these, you can easily detect them indirectly with methods that have a high amount of detectable compounds forming the baseline, though with ms the more junk you put in, the shorter the lifespan of your detector so I wouldn't recommend it (much better with detectors that aren't affected by amount of detection such as DAD).

Anyway, the technical answer is "yes". The practical answer is that software is a tool that makes your life easier. If you have the time and manpower to do the work without the tools, feel free to. You can even do exactly what the software does by hand if you want. I'll leave that decision up to you.