I agree that the multiple oscillators in series are not a problem. Series inverters will not oscillate by themselves without a feedback path. And this circuit has an intentional feedback path synced to the input clock. Unless there is a bad layout, it will not free run oscillate.
And yes crutschow, I know how the circuit works. 30 years ago I knew how the circuit worked. But when someone asks for a non-overlap clock driver circuit the assumption should not be made that they want a circuit that does not overlap the high pulses (or just the low pulses). My first assumption would be that they want matched clock driver circuits that have as close as possible to simultaneous clock transitions. Without any other input that still seems reasonable to me. Maybe you knew that he wanted a slow/medium speed driver circuit that had non-conflicting high times, and it which case, the circuit proposed is fine.
There are still several potential problems with the circuit. One is that it does not work reliably at high frequency input clocks. The variability on the propagation delays of the inverters rapidly approach the low and high periods of the clock. This circuit just wont work reliably at 10 - 50 MHz with standard CMOS inverters. The longer the chain of inverters to seperate the high pulses, the lower the input frequency that it will reliably work at.
The second problem comes into play if the prop delay of the three buffer inverters on one clock drivers are substantially slower than the prop delay of the three series inverters in the the other half. If this difference is equal to the prop delay of the six series inverters, then there is a clock overlap. PROBABLY not a problem if they are from the same logic family, but this can't be guaranteed. Especially if it is a slow logic family like CMOS where the prop delay can be anywhere from 20 ns up to 90ns. This problem requires a lot of things to stack up before it becomes a problem, but it still can be an issue. Especially if this is a mass production design where even a .1% problem is a big deal.
I certainly don't want to turn this into a pissing contest. If this circuit accomplishes what the OP wants, and at the frequency that he wants, then great.
JimW