Lets assume there is a smallest length (time), [itex]l_p[/itex], then at first glance, this appears to violate lorentz invariance, but it doesn't. Pretend there is some length operator
[tex]
\hat{l_p}|l_p\rangle=l_p|l_p\rangle[/tex]
with fundamental length eigenvalue [itex]l_p[/itex]. Then indeed this is the same regardless of the observer, but that is not a violation of lorentz invariance, because quantum tells us that quantity should not change from observer to observer, but rather the expectation value [itex]\langle l_p\rangle[/itex] is an observer dependent quantity. And indeed the expectation value would vary from frame to frame.
Therefore if you treat the quantization of space-time, not only relativistically, but also quantum mechanically, there is no violation.