The ppm error is to account for distance between the base and receiver. There is an upper limit to how far you can be before the ppm error becomes an unsuitable estimate, ~60km.
As far as I understand, the source of the correction ie. internet vs LORA is not directly relevant to the calculation.
The error calc is the same for LORA; however corrections may not be able to be broadcast eg. >8km; so that limitation is a seperate consideration.
Similarly with regards to the skyview, the ppm error estimate assumes suitable conditions. The base and receiver need to have an adequate number of visible satellites that can be seen from both ends and so the usual considerations of working in an open area etc apply.