Pretty much every brokerage house provides online access to the account holder. There is a minority of brokerage houses that provide trustee or PA access to a group of accounts even though each account is titled in the name of the trustees FBO a participant. Exceptionally frustrating to work with.
We work with some plans where the brokerage house is of the opinion that the participant must authorize online access to the account and must authorize mailing a hard copy of the account statement to the trustee, PA or TPA.
There is a minority of brokerage houses that enforce investment restrictions in a participant's brokerage account. These accounts most commonly are restricted to securities tradable on major stock exchanges.
Trustees and PAs do need to monitor investments held brokerage accounts because without the brokerage house enforcing restrictions, the plan winds up with assets like limited partnership, private placements, naked put and call options, real estate, gold bullion and other nontraditional or high-risk investments. We have seen all of these turn up in accounts.
Larger plans tend to require all participants who wish to use a SDBA to use the brokerage house chosen by the Plan Sponsor or PA. Small plans are more likely to allow individual participants to pick their own brokerage house and broker. (Enter into the picture here the owner's recently-graduated children, or Uncle Bob, or Joe at work who knows all about investing...)
Unfortunately, working with a plan that uses a brokerage house that does not provide to the trustee or PA at a transaction and asset level can be a very labor-intensive effort, particularly when a plan is subject to an audit. Further, the plan fiduciaries are not aware when a broker who knows all about IRAs and squat about 401(k)s advises the participant about RMDs or suggests taking a payment and rolling it back into the account within 60 days.
SDBAs definitely can add value to a plan's investment menu. It is important to work with a brokerage house that knows about and provides information needed by plan fiduciaries for the fiduciaries to fulfill their responsibilities.