I would do this:
1- Make sure that your digital levels are correct.
http://glennchan.info/articles/vegas/colorspaces/colorspaces.html

So assuming:
--Vegas DV codec (Not other codecs)
--8 bit project (NOT 32-bit)
then all your levels should be in the studio RGB range. If you have computer RGB sources, you need to convert those sources to studio RGB. Studio RGB sources (most video formats) can be left alone (unless you want to handle superwhites, which is optional).

Add a black solid generator at 16 16 16 RGB on the very bottom track... all fades should go to 16 16 16 RGB in this case.

2- If you are sending them a miniDV master and they are making VHS tapes from that, then you only need to make sure that the levels on your miniDV master are correct. If you have proper digital levels and they have properly-setup equipment, then the digital levels will translate correct to analog and the analog levels will be correct.

Unfortunately, they may not be doing the right thing and might get the digital->analog conversion wrong. (This is because most DV equipment will get it wrong.) So you should check their work if the quality of the VHS is critical. (This might be tricky.)

3- If they are asking for VHS, it may be that quality is not the #1 priority. So it might not make sense to worry too much about quality. The calibration of the analog signal will usually be a little off, so black level won't be bang on even if you do everything else right.

4- It might make sense to apply the broadcast colors filter, on the lenient preset.
Check the 7.5 IRE setup box there (in the FX) if you live in a country that uses 7.5 IRE setup (e.g. NTSC countries except Japan).

If using the Vegas DV codec and the default MPEG2 codec, studio RGB should be checked.

5- The scopes settings are kind of confusing.
The settings there tell the Vegas scopes about the behaviour of your delivery codec + the behaviour of the digital -> analog converter. This way it can make the correct guess about what your analog levels will be.
If encoding to Vegas DV or the default MPEG2 codec in a 8-bit (not 32) project, then check the studio RGB box.
If the digital->analog converter converts digital black level to 7.5 IRE, then check the 7.5 IRE box. However, there is no marking for 7.5 IRE on the waveform monitor... so it's hard to tell what's below black level.

6- Some info on 7.5 IRE setup:
http://glennchan.info/articles/technical/setup/75IREsetup.html