Is some type of sealant required when replacing a sump seal on a Kitchenaid dishwasher mod KUDSO1FLSS3?
No, you do not need a sealant.
Here are your parts
Replacement parts for WHIRLPOOL KUDS01FLSS3 UNDERCOUNTER DISHWASHER | AppliancePartsPros.com
Here is a manual which may come in handy.
KitchenAid KD-01 Stainless Steel Dishwasher Service Manual - ApplianceDigest.com
A light coating of vaseline or white lithim grease can help install it.