I was watching a video ealier were a guy was getting chased by the police, but the police sirens were ELS, and he wasn't using LSPDFR, he was just playing the game itself, not that chase me feature. The thing was his game didn't crash, so my question is, can you actually have ELS activated when not playing LSPDFR and your game won't crash? 

why would your game crash. LSPDFR and ELS are two completely different mods, and are in no way connected to each other whatsoever

Well, a couple years back, I watched a guy who was playing GTA 4 and apparently, having ELS 8.5 activated crashed his game, so I was just curious about GTA 5.  

so you're basing this off the fact that one guy had a dodgy game, but it's not even the same game

Yeah, basically. Now if the mods are unrelated, then I guess it's safe to use then.