Paypal is working with uc_subscriptions via this module http://www.ubercart.org/contrib/4218

The ability to renew subscription and change the renewed duration is something being working on right now. We are changing the logic of a subscription a bit to work with just about anything. For example a customer might buy a monthly retainer of 3 customer support hours. The customer will be able to buy more hours and apply it to the subscription and/or buy more time. You could also sell a subscription of simple 3 hours of support time. The subscription would expire or renew when those three hours are used. Another example is hosting. Because we offer monthly hosting many customer buy one month and want to upgrade both hosting package and length (usually to one year). However, if the subscription expires the hosting account is suspended, so we are creating a way to apply an order to a subscription. Also in development is a way to extend subscription expirations beyond simply buying more. In our tests we are creating ways for hosting customers to link to us and have their hosting expiration extended per click. Or referrals, or blog posts, or answering a support request in the forum...

uc_subscriptions generic subscription doesn't grant the roles. The role is granted using workflow_ng. You can add another condition like "order ballance = 0" if users are granted roles without payment. Subscriptions are registered on a specific order status. If the set to activate status is set to
pending all subscriptions will be registered, paid or not.