Does it matter if RMS meters hit red?

RMS is old school now. You should preferably use a plugin that measures the loudness in LUFS or LKFS. These are the same values only in Europe they use the name LUFS and in USA LKFS. For a target loudness level for Hip-Hop I think they produce very loud like -8 LUFS (that's about -6 RMS) but in general a -10 LUFS value should work okay. However for streaming, mixes sound better if for Youtube are mixed around -13 LUFS or -14LUFS for Spotify because levels louder than these will be punished to a lower level around Youtube or Spotify loudness target. You RMS meter goes to red perhaps because it's calibrated for a lower value or you have imported an mp3 and has some distortion from the conversion.