I am also struggling with this.

The Product is a 1 year subscription set up as per
http://www.ubercart.org/docs/user/3366/selling_site_access_role_promotio...

I have tried Test gateway, set as checked
"Attempt to process credit card payments at checkout".
in admin/store/settings/payment/edit/methods

in workflow_ng I have
"Update order status on full payment" set to condition
"Check the order Balance" <= 0

action
"Update the order status" > Completed

The order goes through, new user created, order set to complete but no role added

Product > edit > features set up as
Role assignment
SKU: Any
Role: member
Expiration: 1 year(s)
Shippable: No
Multiply by Quantity: No

If I set Test gateway
"Attempt to process credit card payments at checkout". as unchecked
I have to go in and process credit card manually and then the role add works

The role also fails to be added using Paypal Standard sandbox (which itself work fine).

My conclusions so far are:
workflow_ng "Update order status on full payment" is working, if I disable this rule the order status hangs at pending

uc_roles only works when I manually process the CC, it does not pick up the process when I set it to automatically complete (which is a 'must have')

Adding another workflow_ng rule "register user to member role" to pick up 'registered user' with 'authenticated user' status and giving it a new role "member" does not seem to work at all. I even added a 'log to watchdog' action after it which *does* work. Bizarre ;-(

My next step I guess will be to add a watchdog line to
function workflow_ng_action_user_addrole()
and see if the action is passing through there and with which $settings

uc_roles writes to uc_roles_products OK though I don't have anything to compare it with.

Any hints on how best to debug this much appreciated