1) I'm not sure. I wasn't even aware of that plugin (it appears to be called "Networks for WordPress") until you brought it up. I'll do some testing and see what I can come up with. At this time, the plugin uses the "wpmn_switch_to_network" function (which is part of John James Jacoby's plugin) to switch between networks; but if David Dean's plugin includes a similar function, I'll be happy to add compatibility for it, too.
2) The roles are managed across all networks, but the Super Admins (and, therefore, the users with the adjusted privileges from this plugin) are managed on individual networks. If a user is only on the Super Admin list on one network, that user will only have Super Admin privileges on that network.
However, it is not currently possible for a user to be a full Super Admin on one network, and belong to one of the additional roles on other networks. The user is either a full Super Admin or belongs to one of the additional roles.
I hope that makes sense. Let me know if you need more information.
EDIT - I've updated the development version so that it should be compatible with Networks for WordPress. If you want to give it a shot (there are a handful of other semi-major changes, too), you can download the Development Version from here.