While there are no initial attack requirements nor qualifications for smoke jumper pilots, carding for smoke jumping is a separate qualification and a pilot must meet the flight time, training, and experience requirements, and time in type, to obtain an OAS/OAM card.
Prior fire experience is helpful for understanding the fire environment, fire communications, the fire traffic area, etc.
Having a prior OAS/OAM card from an unrelated field doesn't necessarily make one more marketable, however, as it has nothing to do with firefighting.
If one is coming from another area of fire, such as air attack or tankers, then moving to a smoke jumper position will pay less, so having an initial attack (IA) qualification over fires wouldn't necessarily be a qualification one would seek before moving to flying jumpers. If one is qualified for initial attack, one would most likely be flying a tanker.
Getting carded for jumpers isn't difficult; one must be qualified, and the card is a checkride with a checked box on the back of the card and a notation. Any pilot who meets the qualifications, undergoes the training, and meets the standard will get carded, so coming from an unrelated field with an existing card isn't necessarily a benefit. It certainly doesn't hurt to mention, however, and if you're coming from a background in which you're familiar with working under a contract, it may be good experience all the same. Time in type would be more useful, however, as would be experience with jumpers, and of course time over fires. Useful, but not necessary.