It's not really a matter of "Can I edit someone else's LR Smart Previews remotely?" but more like this: "if my client sends me a catalogue with smart previews, can I use them to make adjustments and return the work to him or her?"
What she or he will need to do is select the images and do File > Export as Catalog. Checking Smart Previews, but not negatives (originals) will generate a folder containing any work they have done and the smart previews. This will be much smaller than sending you the originals (assuming they are shooting big raw files).
You can then do your adjustments in the catalogue and send it back. They then use File > Import from Another Catalogue to bring your work into their catalogue. That would be it.
It's worth trying (and you could try the above workflow yourself before unleashing it on the client). You may find that you can make good enough adjustments by having the smart previews, but it's also possible that in some cases you'll find them insufficient - eg if you have cropped a high ISO shot and want to be sure about the noise reduction.
Thank you very much for your response. I did a test with your suggestion and it worked great. I am almost in disbelief that someone could virtually send me a whole wedding to be culled through and edited... from anywhere in the world for 2-3gb total. Wow.
Thank you for the answer. Can I add another question on the same topic ?
I know if you send a catalog with the smart Previews the editon also can send you back just the xmp. But I don' know how they do that.