Transiting will not be an issue—they have not enforced the two ticket thing for months. Not sure why they have not updated the site. I have done something similar to what you are doing and United was able to check my bags in all the way to my final destination—even though they were on separate tickets. I have also experienced, where United could not check my bag all the way through—the agent said if the flight is full, they cannot do it because they use a dummy booking to create the luggage tag. I would try to check your bag all the way through which will make your journey much easier.