Kinda. Garbage collection is multithreaded, and some small things in MC are multithreaded, but none of the important stuff.
Also, MC 1.7 might be single threaded in most of his code but that doesnt mean mods are single threaded!
In DW20 1.7 I clearly note an higher use of my CPU, not that its poorly coded. On the contrary, it seems to be better optimized. Since most of 1.6 execution was single-threaded, the most CPU it could use was 25% since I have 4 cores and it was only using one core. Now I see the CPU going to 50 or even 60%, so it means something is launching other threads and using the other cores being more efficient. With Java 8 optimized garbage collection and thread management, it just becomes awesome!
After I installed Java 8, I havent tested the pack with Jorney map to see if I still have problems but in my opinion, the pack should come with Opis by default, a starting screen warning advising to install Fastcraft (this is possible with a small mod) and the FTB Launcher should be updated to advise players to install Java 8, the same way they advise to use Java x64... (since this affects every 1.7.10 pack)
Now... we only need to find out what is leaking memory (the reason Java crashes after 7-8 hours of gameplay). It can be a mod or it can be MC himself(the dimension leaks for each there might be no solution)....