The capacitor divider in an half bridge LLC is to reduce inrush at startup.
If you use a half bridge llc driver to drive a full bridge llc, then you need to drive all 4 fets through a similar pulse transformer…..this is because you need the delay to each fet to be the same, and as low as possible…..this is because the dead time is important in llc converters…..specially at light load when the frequency goes high….you need to have enough dead time to allow enough magnetising current rise to enable zero voltage switching.
i think infineon possibly do a full bridge llc driver but i could be wrong.
Also you can use bootsrapped high side drivers too, yes.
You cannot use optos to drive llc fets...optos are just too slow.
Whatever you do the driving with, you need it to be the same for each fet.... or rather, the delay to each fet must be the same, AND LOW ENOUGH DELAY NOT TO AFFECT YOUR REQUIRED DEAD TIME. (sorry about capitals)