You should be able to do both. There is evidence that nematodes are tolerant to many herbicides and fungicides, although they are sensitive to certain insecticides and nematicides. Look at the label for more information. As for your use of a preemergent, most are of low toxicity, but do read the label carefully for all directives about reentry and so on. Also make sure there is a need to apply the product and that you are doing it in the right time frame for efficacy.

Sorry it took so long to say thank you for this!