Exploits definitely not, Embeds probably not.
Page 139 of Flowers of Hell: the Demon Player's Guide says the following:
Instead of priming the object with Aether, the demon simply
pulls forth the Exploit and pushes it onto the object until it bends
under his will.
As a result, creating an Exploited Gadget without knowing the Exploit the Gadget is going to use is definitely impossible. By contrast, the segment on the creation of Embedded Gadgets on p. 138 of that book implies that the Demon needs to know the Embed, but doesn't explicitly state it:
Once the item is primed, the demon concentrates on the
specific effect he wants to Install in the object. He pushes the
item towards that effect as he simultaneously pulls the effect
into reality. Alignment of the two dictates the exact effect the
demon can Embed in the gadget.
In order to "pull the effect into reality", he'd presumably need to know the Embed in question, so I'd definitely rule that they do need to know the Embed in a game I was running, but the book doesn't explicitly say that they do anywhere I can find.