Using the Univibe as the only effect in a guitar setup will mean that overdrive will be created at the amp, after the signal passes through the Univibe. In the early days of guitar pedals, it was not uncommon for a musician to have only one effect and to rely on the amplifier to provide distortion, often at very extreme volume. While your ears should be the final authority on best placement, a Univibe ahead of the overdrive and distortion stages is probably not the best location, as the Univibe effect may get buried.
When using several effects, one connected to the next in daisy-chain fashion, there is a good starting point for ordering effects which places filtering effects like wah pedals first, followed by overdrive and distortion devices, which feed modulation effects and finally delay and reverb pedals. The Univibe is considered a modulation effect, so this rule-of-thumb puts the overdrive unit ahead of the Univibe.
Parallel chains can take advantage of mixing a clean sound run through the Univibe with a distorted sound of an overdrive unit. The guitar signal must be split and routed to two signal paths, then run to separate amps or re-combined and sent to a single amp. Combinations in such a setup are varied, but this lets you treat each half of the signal independently. Again, let your ears and taste guide you.
The Univibe is suitable for use in a guitar amp effects loop. Effects loops are placed between the preamplifier and the output amp, so two stages of overdrive, both before and after the Univibe, are possible. This arrangement is a variation on a parallel chain and may be a suitable solution for you.