That is correct. Combining two CE certified parts into a new product requires recertification. If you buy a wifi dongle that is certified as a product and you use it on a computer that is certified as a product, you are not making a new product. You are using it in the way it was certified.
If you put a CE certified RHF0M301 or RN2483 on a custom board and connect it to a CE certified RasPi, you are making a new product. If you connect a CE certified antenna to a CE certified gateway, you are making a new product.
The gotcha is that parts like RHF0M301 of RN2483 are only certified as radios, and not as the end product we want to use them for. If they want to be CE certified as products, they need to sell the radios and the antennas used during certification (and, if applicable, soldered on the PCB they used) all together as one package. Most manufacturers clearly state that their CE certification is only for the component itself, not for the application it will be in and that it is the responsibility of the integrator to certify the end product as a whole.
E.g. a wifi router is only certified if you use it with the antennas it came with. If you swap antennas, you have made a new product (even if those antennas are CE certified) and need to do new certification.
I have stated on several occasions that the lack of certification, be it CE, FCC or LoraWan Alliance, is the Achilles heel of TTN. People are taking this issue way to lighthearted, e.g. in this thread, just running aloft with totally uncertified radio modules, protocol stacks, antennas, transmit power, duty cycles etc. I’m pretty sure that it would only take one cease & desist letter from a major telco to shut the whole thing down, even if TTN is not the ultimate responsible party. TTN may have a small war chest from the kickstarter, but it is in no way able to pit legal fees against a telco.