"Is the 7D a camera that could replace something like the HMC150 or only used to support it?"
Could it replace the HMC? Yes, it could.
Should it replace the HMC? IMO...No, it should be used WITH the HMC as another tool.
"I heard about concerns with the audio on the 5d II but supposedly these were addressed on the 7D. Does the 7D have XLR inputs or will it require an adapter?"
Your question has been answered on the XLR jacks and the AGC undefeatable. However...if you've been shooting video for a while, you also are most likely used to second system audio recording...Zoom, Tascam, Sony, et al. make great portable, solid state, 4 channel sound recorders with XLR and built in mics. Certainly not a deal breaker on buying a camera in my opinion...buy the camera for the video...Best sound is NEVER recorded to the camera.
"Should I decide between one or the other or is it wiser to purchase both?"
Can you afford both? If so, sure...buy 'em

But, as mentioned, there is more to it than just buying the cameras. Support, audio, media, mics, light, cords, Pelicans and stands....the list goes on. Obviously, you need to buy glass if you opt for the 7d...and you will defeat it's low light possibilities by going for anything less than 2.8...and much faster in the case of primes. There are, however, a nice range of "used" Nikon glass (Primes) that can be fit to your Canon with a lens mount.
If it was me (and I, too, shoot 5d2/7d HVX200a/EX-1 combos)...I personally would start with the 150 and all of the necessary support, light and media to get it up and running. You'll be a happy shooter initially...where as the 7d can be a frustrating assignment (shooting video) in the beginning

(and that's an understatement).
I love my DSLRs...but, while they do have strengths that are hard to replicate in anything other than VERY expensive cinema cameras and lenses...the negatives far outweigh those strengths while getting up to speed on making the camera work for you. These DSLRs do not focus on their own...and they are damn near impossible to keep stable handheld...viewing the LCD is an act in and of itself trying to run and gun....and lighting, audio, etc... Well, you get the picture

Don't want to disuade you from the purchase, but rather, warn you that the footage you see...online that looks great, took a LOT of work to get it that way
Good Luck!
jer