depends on how you render. Yu shouldbnt realy concern yourself on hwo it looks on your ogl preview (after all its just preview). Personaluy i had no big problems in rendering complex cad data.
1) use micropoly rendring
if you rendr with mr then you can allways use the fine tesselationa ttribute that should with enough precicion on part of the object patch alignments do the tesselation fine.
If you render in prman no prob the tessleation is by default worked in away wish wll handle this better.
2) tesselate smarter
If you render in maya internal renderer or are foced to use some stupid tesselation scheme in mentalray. Then you can use the smooth edge at a value of 0.999 or if its not enough beyon (it is possible to boost this because its a spatial effect so if you scale by 1000 and freeze scale back down by 0.001 but dont freeze), youve pumped this to 0.999
3) tesselate over seams
Mr can do thsi the thing is that ist a bit hard to accomplish... Also mr is phasing out of thsi way of doing it.
Okay then a word about iges import! its very precicion sensitive, both your maya precicion and cad precicion matter much here (and scale). Also note taht angular precicon might differ from normal dimensions. Ive had some problems regarding this in pro|e and radial arrays in wich the error accumulates (but i can collapse the array and refeer to one angle to make the problem dissapear), because i have no direct controll over the engular tolerance.
Personaly i feel that the new step translators and otehr cad connecxtors have been a much desired change here. After all iges is age old and a bit creaking by age, and is allmost obsolete.