Hey Switchback, welcome to the forum! I'm seriously considering putting the RE as my first choice come RSB as it seems to offer a mixture of variety of roles whilst still be close enough to the sharp end. I'm also an electrician on civvy street so i have a general knowledge and interest in construction, engineering etc.
I recently attended the RE fam visit so i'll make an attempt at answering your questions. In regards to your question if candidates with degrees in non technical subjects are disadvantaged my answer would be no. I stand to be corrected but i'm pretty certain your able to join whichever regiment you want to join, within reason.
The advantage of having a degree in certain technical subject and joining the RE would be that your able to attain chartered engineer status if you so wish.
Your certaintly not going to be disadvantaged though, leave that for mugs like myself who don't even have a degree! In all seriousness i highly recommend getting yourself on the RE fam visit, it will answer all your questions and it's a good laugh as a few members of this forum will tesitfy.
I'm sure there are better placed and informed people to ask but if you want any advice PM me.