CVS vs SVN could 2 or more developers (1 using SVN the other using CVS) do so in a working environment effectively??
If the half team was using CVS and the other half used the other SVN say like in a competition to see which will dominate and become the winner thus the last repository standing the question is...
Could both teams connect to the same repository without screwing something up royally??
Well there is a migrator tool for migrating from cvs to svn but I don't think it allows you to merge the projects while importing. You could try import the CVS repository as a branch into SVN and then merge it with the trunk. But basically it is not the best idea to use two different VCS for one project. Maybe you should have a look into one of the Distributed Revision Control Systems as well.
You can try to use cvs to svn bridge but I strongly recommend to switch to SVN. CVS is dead. Don't touch the deceased.
Could both teams connect to the same repository without screwing something up royally??
Nope.
Besides, CVS is deprecated so if you have a choice between the two, use SVN.
Simple answer is no. You don't want to do this. Even if you could hack together a solution, it will be riddled with inconsistancies. Do you really want to take such a risk with the most critical asset you have (your source code)? Just go for svn.
In order to use both tools, you need a replication system so you can have a cvs and svn repository both represent the same source code. None such tool exists for cvs and svn--there are migration tools, but not meant for live replication.
git and svn are different, git was designed with this use case in mind to allow individual developers to choose to use git when the company/team uses an svn server. This is very unusual though, I'm not aware of any other type of live interoperability between source control systems.