Of course they can.
We often use Sage RPLXi's for Sea Trout fishing in 6wt and 8wt's.
They were designated at saltwater sticks.
We also use spey rods in the salt (moving water of course).
You don't want to get bogged down with advertising.
They'll tell you you need a different rod to throw both white
and yellow clousers if they had their way.
A saltwater rod will usually have more resistant hardwear and maybe
have a different shaped handle.
That said, find a wood turner or do it yourself.
I changed my RPLXi 6#wt to a half wells with a bit of thought and
careful pre practice.