How it the money got there isn't actually, the issue.
It's the NATURE of what the account is today, a SEP.
And the the SEP is an IRA.
The SARSEP (Salary reduction SEP) is still an IRA.
401(k)'s are ERISA
plans (subject to ADP and ACP and many other tests by IRS As WELL AS MANY other tests relative to plan document, employee communication and education , etc. by the Department of Labor)
SEPS are just a super IRA and don't fall under ERISA Labor Law
IN, fact Salary Reduction SEPS were eliminated (better said, getting money into a SEP via a salary reduction was eliminated) to, among other things, more clearly separate SEPS as an individually owned, non ERISA, always automatically vested, IRA plan.
SEPS are IRAs.
A SEP, for example, doesn't have true plan document, as an ERISA plan does, one simply fills out a 1/2 page 5305 form, and that's it.
Here's how IRS puts it: from http://www.irs.gov/Retirement-Plans/Retirement-Plans-FAQs-regarding-SEPs
"A SEP-IRA account is a traditional IRA and follows the same investment, distribution, and rollover rules
as traditional IRAs."
Hope this helps,