Summoning Mobs With Players Rotation
Solution 1:
To get the exact rotation (rather than what Darkchill Slayer answered) you summon it with a certain tag:
/summon pig ~ ~ ~ {Tags:["Rotate"]}
And in an always active repeat command block:
tp @e[tag=Rotate] @p
This will not only teleport to the same location, but also with the same rotation. After the repeat command block you should add a chain command block:
scoreboard players tag @e[tag=Rotate] remove Rotate
This prevents it from always teleporting to a player