Can I use the Omron G6RN relay where reinforced insulation is needed beetween coil input and switched circuit?
You should be fine from an electrical hazard point of view with that relay. Reinforced insulation can not be faulted. IEC 60950 is a single fault safe standard, so any 1 means of protection or and 1 component may be faulted to a failure mode, which cannot cause a hazard.

With reinforced insulation, you have 2 means of protection from the hazardous voltage. If you fault one, you still have a second means.

If a fault could occur where the relay could be continuously energized, and the motor runs and overheats, you could have an issue there.

As far as your question on the interpretation of the relay, one thing you can do is to lookup the VDE or UL certification, or request the certificate from the relay manufacturer. A quick google search will bring you to the VDE or UL database.