I would not worry about different products working together as long as you read and follow their prep rules.
You should use the right product for each job.
Use the Interlux Watertite for divot filling, two layers, the first a rough fill, the second a careful level fill, as it is a bear to sand.
Use West epoxy with microballoons for fairing as it's very easy to spread and sand.
Interprotect 2000 is specialized for barrier coating, it set ups slowly and is easy to roll. West does not make a barrier coating product, although their epoxy doubtlessly makes an excellent barrier coat - if you can get it not to cook up fast, and develop a good roller routine. I have to admit, I never tried to overcome these challenges, the Interprotect to too good at it what it does to struggle with regular epoxy.
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