No seems the more logical answer (but the memory can still be removed)
First off, yes, Pacts are a little fuzzy around the edges, and no official material states "Pacts can be for memories" nor "Pacts cannot be for memories". Ergo, an ST may rule differently without being wrong, but my analysis concludes that memories can't be included in Pacts:
A Pact is, in essence, a trade, where a Demon get descriptive characteristics for a Cover, and the Pact-bound gets (most often) a quantifiable advantage; bound in a physical artifact.
A "descriptive characteristic" is some means of fooling the GM's surveillance; kind of like an alibi. "I can't be the Demon you're looking for - I'm the vice president of sales, not unemployed!" or "Sure, that looked like a possible cover for that Demon, but they have a pet Siberian tiger. There's no way we overlooked that; we must have the wrong guy." All these details, expressed in Cover Experience.
Ergo, to have "Remembers they made a pact with a Demon" as part of the gains the Demon obtains seems counter-productive - like saying in a police interrogation, "Officer, I couldn't have shot that man - because here's a video of me shooting a different man with the same gun!"
From the Pactee side, most of the benefits are things that affect their sheet; in the "brilliant painter's" case, some dots in the Crafts skill, maybe a skill specially in Painting (maybe a dot or two of the Fame merit to "cut to the chase", if you will). It's also possible to remove some persistent Conditions, like being blind or disabled. Given that there is no Condition of "Knows they have signed a Pact with a Demon", such an effect isn't possible for a Pact.
Full disclosure: age can traded in Pacts, and isn't mechanically represented on a character's sheet; I feel that the difference between age and memory is palpable in that age can be casually observed, whereas a lack of a certain memory can be much harder to discern.
All that being said, can a Demon prevent their Pactee from remembering their pact? Sure, there are a couple options, in ascending severity:
The Embed Never Here could, while made at a steeply penalized roll, cause the Pactee to be left with the knowledge that a Pact was signed, but not with whom.
Muse could be a more insidious usage; implanting "I dreamed signing an agreement with a devil, but I've been this talented all along." Rather like in the movie Inception, turning the Pactee's mind against their own memories.
But, nothing's going to beat the Process Memory Theft. Just make sure you block out enough time afterward.