Would not even think about it... great amps, the DRRI you can get them anytime... pros, great sound, great tone and a great vintage amp, the cons... may need new tubes and caps and some service... still great trade...
The Vibrolux is a better gig amp, can stand up next to loud drummers, where the DRRI will struggle (ask me how I know). The DRRi is a great amp, don't get me wrong, I loved mine. It was pure rock and roll, or country or blues... it had a great snarl and it was loud at practice and such, but the minute I did na outdoor gig, I was kinda fighting it a bit...
The Vibrolux, not so much.
I sold off my DRRI earlier this year and replaced it with a '63 Vibroverb Reissue. I love that amp and don't see giving it up as my main #1 any time soon. However, i had the opportunity to pick up a '69 Vibrolux and didn't have to think about it for more than about a split second. I know this particular amp and know it won't need anything any time soon. It's been well cared for and not played a lot since it's last service. But, I also know how good the darn thing sounds! That's enough for me.
Vibroluxes and the other 2x10 35-40 watt Fender amps are probably my favorite amps out there. They fit well, the 2x10 setup is good for guitar and sits good in a mix. They can be loud in small rooms, but they don't struggle in larger venues.
The Vibrolux (BF/SF) breaks up nicely as well.
Plus the VR is probably worth two and a half to three times what the DRRi is worth on the used market.
So, uh yeah, go for the trade and don't look back.
^Looks pretty unanimous. I'll throw in too, as I've owned 2 DRRI's and currently have SFDR and SFVR. The SFVR is a fantastic amp, if you are offered a trade you should consider. Not writing off the DRRI, it's a fine gig worthy amp...but play it beside the Vibrolux and see what you think. Personally I would take the offer. Even at low volume the 'lux will give you shades of SRV & Buchanan!