Several different issues being addressed, so my 2 cents on each.
As far as extra par, yes, the T5s will give you extra par. However, you may not even need the extra par unless you're already at full intensity on the radions. Adding an extra LED unit might provide the same type of bump in par you're needing, though. But if you have a really long tank, the t5 bulbs can sometimes be a little easier versus trying to buy extra led units and spacing them closer together.
As far a quality of light, some people might say T5 bulbs provide better spectrum coverages. I'm really not sure about this claim. I think modern led manufacturers have done a pretty good job of using appropriate LEDs to provide needed spectrum and in appropriate proportions that will grow corals very well. There are plenty of LED only tanks out there that can attest to this.
Visually, the T5s will make the tank look different. It will be more diffuse than just LEDs, and it will reduce the disco ball effect and make shimmer less noticeable (but will still definitely be present). Some people like the combination, some people don't. I like both. I love my leds for shimmer but I love the diffused light source with the t5s. I love the programmability of my LEDs- dawn / dusk options and ability to easily ramp them up and down throughout the day as needed is nice.
As far as shadowing, I think T5s provide a more diffuse light source and do reduce shadowing which can be of benefit in tanks with larger coral colonies. If you use enough LED units or use led units that utilize more spread out configurations, then I believe this can address shadowing issues also.