Depends on your intent, and also how you're interacting in the comments. If you're appreciating the other person's video, then are they really a competitor? Or are they simply someone in your niche that you can build a friendship and possible collaborations and community with in the future?
If you're in their comments responding to OTHER people's comments, in my opinion that's tacky and poor form.
The fact you call them "competitors" is slightly telling, but then again, that just might be the word some use for "others in my niche"
Just know that the videos you're commenting on, they WILL see, so if your heart is in the right place, they will know this and appreciate you and potentially reach out at some point, or at the very least appreciate you being part of their community. But if you have alterior motives, they can usually see that. I've had a number of people try to "poach" my viewers away from my videos which is pretty shady behaviour. HOWEVER, there are some pretty established artists in my comments who genuinely like hanging out with me and chatting. I have absolutely no issue giving them shoutouts and integrating with them because they put the human factor before the "growth" factor. You always rember those who just want to connect, and who only want something to benefit them, even if that benefit is self publicity.