Frame acquisition vs symbol timing synchronization For a known length of frames  and using a known sequence in a preamble that is also  of known length can auto correlation at the receiver  be enough to acquire timing or is timing synchronization at the symbol level still needed?
Auto-correlation will be enough to determine the symbol center of 1 symbol at the end of the preamble, so that is sufficient for acquisition.

Symbol center tracking throughout the frame is still required to keep the receiver symbol clock synchronized to the transmitter's symbol clock.  Your receiver's symbol clock frequency will never be exactly the same as the transmitter's symbol clock frequency in real implementations, therefore continual estimation and correction or tracking is needed.