There is a small caveat to the replay mod. It will only record anything within your render distance. If you keep it high it shouldn't be a problem, but if you have another mod (specifically optifine) you may have issues, as to my research, they seem to cut player rendering distances to preserve some framerates when possible, so while the world might be loaded in the replay, you may have a hard time recording a hacker that is across the map. However if your computer is good enough to handle minecraft without optifine, then that's great! Because the mod barely does anything on damaging framerates!
However if you get into close encounters with any hackers, you'll be able to get them just fine.
I recommend also going with the BetterFps mod if you need an optifine replacement, I haven't tested this for player render distance however, so I am not sure if it's better or worse.
tldr; Keep your render distance high, maybe keep optifine away, and you can probably record the entire game!