To give you a simple answer to your question.....No.
You're pretty full as it is now with the GT, JD, and O and if the Jewel's happen to be a mated pair and happen to mate you are going to have quite a bit of trouble.
RT's get quite large and are quite nasty and wouldn't do well with the group you have. And this isn't even considering the "mystery" fish you have.
A couple of other points for you:
1. What kind of pleco do you have? Some commons can get quite large, upwards of 24" long
2. Blueberry Oscars do not occur naturally. They are a regular oscar dyed to get that color. The dyeing process is often quite stressful and the process alone kills many fish. Those that survive are often left weakened by it and their life span is dramitically shortened. A normal O can live 10-20 years, you'll be lucky to get 2 out of yours, I'd count on 6-12 months. If that isn't bad enough for a fish you probably paid decent money for the color which drew you to him will gradually seep out of your O leaving you with a pale, greyish, sickly looking fish in about 6 months.
You should have this information so you know what to expect. If I were you i'd take the fish back and demand your money back.