I want to know if tethering with my Xperia Neo V via USB will affect the battery capacity in any negative manner other than the usual.
No. There's no relation between those two things.
If you connect your phone via the USB it gets charged. It doesn't matter if you don't use the USB connection at all or transfer files or tether your data connection or do any other stuff while it's connected.
The charging circuit doesn't even know that it's connected via USB and that there's data flowing. It just happily charges the phone with the power supplied via USB.
Side note: The battery (LiIon) degrades over time, if you use it or not. There are however differences in the speed of degradation, depending on usage, storage temperature and charging state (best is around 60-70% charged as far as I know). This is however the usual degradation which you asked not to factor in. And this degradation definitely doesn't change if you tether or not.
yeah it would certainly shorten your battery's life. Every battery has a maximum number of charge-discharge cycles. So when the phone is tethered via USB, battery is charging. The more FREQUENTLY you charge your battery, the more you shorten its life. This applies not only to tethering/data transfer, but also to the habit of many of charging phones for a short duration, then again discharging it , then again charging it. This drastically reduces the battery's lifespan.
The best habit is , Charge the phone to 100% . Then use it till its down to 15-20%. This is the best time when you should plug in your device. Mind that discharging to 0% also has adverse effects on backup of a battery.
So IMO Bluetooth tethering is the best solution for 3G speeds.. It is available since ICS . If you want to utilize full 4G speeds, prefer WiFi tethering. While tethering, when the phone's battery comes down below 20% , consider charging it. It's always handy to carry a spare battery with your Droid.