The Display Only OEM probes do not include the stands, etc for print reading, but can be used for printers if you can read the printed colours without those components.
No 'restrictions' at all, except for the components supplied.
(See the list of components supplied with the i1 Pro 2 Display Only OEM probe here: http://www.lightillusion.com/i1_pro_2.html
The probes come with all standard X-Rite guarantees and support.
The C6 is basically an i1 Display Pro, so is a Tri-Stim device, and not a spectro.
(The standard i1 Display Pro does OLEDs too - nothing special with that regard.)
As for measuring OLEDs it is more down to the software (LightSpace CMS) rather than the probe.
(Although the probe will define the accuracy in the blacks, and such low-cost probes will never be that good, especially with OLEDs - we prefer the Klein K10-A as it is much better in the blacks!)
Mob Boss at Light Illusion