I wouldn't connect the RO line directly to the float valve. I feel like it's a recipe for disaster should the float valve fail. TDS burst will also exhaust your resin fast.
If I were considering plumbing in the RO line, I would plumb it into the resovior and have some safety mechanisms in place with the Apex. For example, use a level sensor or high/low float switches/optical sensors in the reservoir to control when a solenoid opens/closes the RO line. Maybe a pan under the reservoir and sump area with a leak detector as a back up to shut off the solenoid and alert you. You can even program a max time the solenoid can be open while filling the reservoir with an alert/shutoff.