Yes, there is a chance.
But, you won't know until you check the bag at SEA and that is way after you have purchased the ticket.
As others note, 90 minutes is not enough time to retrieve your bag, drag it to UA, check it in with UA, clear the checkpoint and head to your new gate.
Consider using UPS or FedEx Ground for your bag. Depending on its weight, it ought to cost $25-40 and will take around 4 days. That way, no checked bag and you still get the cheaper fares.
But remember, if your inbound flight from SEA is late and you therefore miss your UA flight, your UA ticket will be cancelled and you will be at UA's mercy to get it reinstated (or purchase a new one).