Think of the "sealed" setting as a holdover from the old days. What matters is the voltage set points and the charge profile. Depending on who made your AGM battery, even 14.4v might not be high enough to be truly optimum. Good enough, and better than 14.1v, but still not perfect.
I don't know of any AGM manufacturers who recommend *less* than 14.4v bulk. Or, at least, can't think of any off the top of my head.
So, yes, I'd run it at 14.4v.
As to whether that will have any effect on the problem with the indicator light. I can't say. That problem could be caused by any number of other things - loose connections, a dodgy fuse or fusible link, alternator going bad.
Generally, two different charging systems hooked up to the same battery do not cause problems for each other. They each do their own monitoring, and each supply power when they detect a need for it.
If the voltage regulator takes the battery up to 14.2v and the sun comes out, then the SunSaver will see that 14.2v is not high enough, and go ahead and start charging.
If the SunSaver takes the battery up to 14.4v and the voltage regulator is set for 14.2v, then the voltage regulator will decide the battery is charged and not turn on the alternator.
If the voltage drops below 14.2v, then they'll both be supplying power until the battery gets to 14.2v and the voltage regulator shuts down the alternator, and then the SunSaver will stop charging when it decides the battery is full.