*** edited for clarification.
That is correct - Canadian-domiciled ETFs that hold US ETFs or individual US stocks are still subject to withholding taxes, even in an RRSP. Thus, ZSP.U, even though it is denominated in US dollars, is still subject to withholding taxes in an RRSP.
Holding a US-domiciled ETF that holds US stocks or ETFs are not subject to withholding taxes in an RRSP.
As of our latest knowledge, ZSP and ZSP.U have two different Cusip codes and thus a broker is not likely to be able to treat them the same and journal them between accounts.