Assume a plan holds an interest in a private venture capital fund. Do the ERISA bonding requirements apply to those individuals who invest on behalf of that fund?

Depends on the application of the plan asset rules, ERISA Reg. section 2510.3-101. The offering memorandum for the fund should discuss the issue.

Meaning if it qualifies as a "plan asset" it needs to be bonded?

If what qualifies as a plan asset? The regulation applies to determine if the plan is treated as owning only the LLC interest or if the plan is treated as owning an undivided interest in each of the assets of the LLC. If the latter, then one of the consequences is that the person that manages the assets of the LLC also manages assets of the plan.