Hewoo!
Edit1: Sample = sound that you recorded.
I'm not really that good with this kind of thing, but I think I can help you with smth. Starting with an answer to your deepvocal question Idk for sure, but I'll be honest I think yes although I recommend you to start with utau (Just bc you have more content and bc I preffer it).
First you have to decide what voicebank do you want to record, if it is a CV, VCV, CVVC, etc. As you said Arpasing is actually considered by the community as the best english method, but it doesn't mean that others recording styles(methods) are bad too. Tbh Arpasing can be really hard to do if you don't have much experience with utau. Considering that CVVC and VCCV (A method created exclusively for English vbs that you can found more information here:
http://utau.us/vccv.html) are really good recording methods and they have both languages support you just have to search their reclists.
What I really recommend you to do is search a reclist that support both languages to the method that you chose, but if you don't find it you can use two reclists (One for English and another one for Japanese) to record your utau. You can use preffixes to differentiate the languages. Preffixes are characters that we write after or before the sample's character to differentiate same samples sound for the utau. For example: If you record "Ra" in C5 but all your others samples was recorded in C4 pitch (Even a "Ra" sample recorded in C4). But this can turn your vb hard to use and confusing depending on what you want to do with your utau.
But there's a better solution to this. Here where I live an utau creator made a method to record portuguese voicebanks using a language named by X-Sampa. X-Sampa is a language created to the phonetical international alphabet, Idk much about it, but if you can't use X-Sampa you can name your utau's sample with the International Phonetical Alphabet (IPA) to the English language and name japanese samples with the IPA/X-Sampa symbols. Obviously that the sounds that both languages share between them can be writhe in a normal way without using any symbol, doing this you will help your utau's users to have less trouble when they're going to do an utau ust.
I hope I could help you, if not I can explain to you better latter! ^^ Thank you!
See ya~