I have done some testing and as for now I am close to be certain that GCD works on CC. Animation can be little confusing from time to time, but it was exactly same with P/S`s Ice Blade.
Currently I have manage to cast 102 CC on 120s period with 1 mana potion and 67 other skills (27xUnT, 26xASE and 14CrC). So cumulated 102566,4 DPS points (in reality little less due to double hits from ASE), instead of 120 CC and 85248 DPS points from not using combo and theoretical maximum of 120CC, 30 UnT, 30 ASE and 20CrC and 120896 tDPS points (little more again double hits from ASE). So somewhere in the middle and 20% better than spamming CCs.
Probably better score can be achieved, but as I mentioned before from my testing CC and PotWS also suffers from GCD from other skills, also as for me there is no possibility of using 2 skills in gap shorter than about 0.200s (server/connection problem), so comboing means that I am close to my maximum regarding CCs (as with not efficient number of skills to not wait for CDs I still probably have some space).
Getting back to combo 0.2s lag I mentioned means any skill used during CC cooldown should make more than 20% of CC DMG, so with shot it would be:
T12 2h bethomia Axe - 4916,3 DPS + 50% passive +20% passive + Power of the Oak = 10176,7 DPS
10176,7*7,104*0,2=14459
T8 Bethomia Crossbow - 4574,4 (incl. speed passive) + 41,8% from blood arrow = 6486,5 DPS
6486,5*2,368=15358
Remaining buffs are same, so I simply skip them.
So we have 15358 vs 14459. Of course difference can be bigger, if lag would be smaller (and I have calculated numbers from 0.130 to 0.250, probably 0.142 from my M/WD 70lvl elite skill testing few days ago - but I do not suppose can maintain so close on any skill rotation and even during that test it was the smalles value vary from 0.142 to 0.182). Still there is a question if there is a reason of using blood arrow and what will our healers say about it, but I will agree that raw numbers look promising and with smaller "mini GCD" break trough number is 10265,9 instead of 14459, so we will have 15358 vs 10265,9. How much it will change on the end of the fight.... Probably close to nothing, but if someone wanna try.
As for other skills there is literally nothing to use. Point based focus skills from scout simply do not benefit from raid runes, stimulant, lute etc. so especially during burn are useless, after burn takes almost 3x more "mini GCDs", so instead 0.2s, 0.6s for same amount of focus used, focus/DMG ratio is only about 50% better, so I still wouldn't recommend them at best it would be same DPS as UnT alone. Anti-Magic Arrow is simply focus eater. Skill set from DL/ZS is cast based, so we loose 1 CC+skill can be interrupted. Thorny Vines DoT is useless have it on +0, but I do not expect any huge improvement from lvling and this is 2x smaller DoT than on VA, where is also start DMG....
Making long thing short will probably still stick to Va+UnT+ASE adding CrC and FB on full burn bosses, where there is possibility of using AoEs.