T-5 Spacer

Not sure what you mean. If you are switching to a cable, then it should mostly be a bolt in swap. If you are refering to the plate spacer that goes between the trans and the bell, then no. The T-5 bell is the correct depth. The spacer plate is if you want to put a T-5 into an early bell with the equilizer bar and clutch linkage.
I am making a broad assumption that you are using the fork that came with the T-5 and associated bell...you will need the T-5 fork to work with the cable.
 
No, you do not need the spacer for the fork if you use the T-5 bell and one of the cable clutch conversions. There are several and each has its proponents/detractors. The Modern Driveline cable works well, but replacement cables are pricey. MustangSteve's works well, also, according to some here. The major drawback is in header choice. Many headers designed for z-bar clearance will not work with the cable, or will have tubes too close and melt the cable housing. I had to have one tube altered to make mine work, and I use a heat shield. I really love the clutch actuation now, however, and really do not like the hydraulic clutch on my 2006 GT. I'll keep the cable, thank you very much.